Exposure apparatus having projection optical system with aberration correction element

ABSTRACT

A static image distortion characteristic is averaged in the width of a projection area in a scanning direction and becomes a dynamic image distortion characteristic, when a mask pattern is scan-exposed onto a photosensitized substrate by a projection exposure apparatus. At least a random component included in the dynamic image distortion characteristic is corrected by a arranging an image correction plate obtained by locally polishing the surface of a transparent parallel plate. Correction plates which minimize other aberrations beforehand are manufactured and installed within a projection optical path, considering that also the other aberrations are averaged and become dynamic aberration characteristics at the time of scan-exposure.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.09/488,570, filed Jan. 21, 2000, which in turn is a continuation ofinternational application no. PCT/JP98/03305, filed Jul. 24, 1998, whichis incorporated by reference in this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exposure method and apparatus foraccurately exposing a sensitized substrate with a pattern formed on amask through a projection optical system, and is particularly preferablefor a scan-exposure method used in a lithography process formanufacturing a circuit device such as a semiconductor circuit element,a liquid crystal display element, etc.

2. Description of the Related Art

Currently, on a semiconductor device manufacturing scene, astep-and-scan projection exposure apparatus which scan-exposes the wholeof a circuit pattern of a reticle to one shot area on a wafer, by usingan ultraviolet pulse laser beam having a wavelength of 248 nm from a KrFexcimer laser light source or an ultraviolet pulse laser beam having awavelength of 193 nm from an ArF excimer laser light source as anillumination light, and by performing one-dimensional scanning for areticle (original version, mask substrate) and a semiconductor wafer, onwhich a circuit pattern is drawn relatively to a projection field of areduction projection lens system, is a promising exposure apparatus formanufacturing a circuit device.

Such a step-and-scan projection exposure apparatus has beencommercialized and marketed as a micra-scan exposure apparatus which isequipped with a reduction projection optical system composed of adioptric element (lens element) and a catoptric element (concave mirror,etc.), and is provided by Perkin Elmer Corporation. As explained indetail, for example, on pp. 424-433 in Vol. 1088 of SPIE in 1989, themicra-scan exposure apparatus exposes a shot area on a wafer by scanningand moving a reticle and the wafer at a speed rate according to aprojection magnification (reduced to one-fourth) while projecting partof the pattern of the reticle onto the wafer through an effectiveprojection area restricted to an arc slit shape.

Additionally, as a step-and-scan projection exposure method, a methodcombined with the method which uses an excimer laser light as anillumination light, restricts to a polygon (hexagon) the effectiveprojection area of a reduced projection lens system having a circularprojection field, and makes both ends of the effective projection areain a non-scanning direction partially overlap, what is called, ascan-and-stitching method is known, for example, by the Japaneselaid-open Publication No. 2-229423 (Jain). Additionally, examples of aprojection exposure apparatus adopting such a scan-exposure method aredisclosed also by the Japanese laid-open Publications No. 4-196513(NC:Nishi), No. 4-277612 (NC:Nishi), No. 4-277612 (NC:Nishi), No.4-307720 (NC:Ota), etc.

With the apparatus which restricts an effective projection area of aprojection optical system to an arc or a rectilinear slit shape amongprojection exposure apparatuses of a scan-exposure type, an imagedistortion of a pattern transferred onto a wafer as a result ofscan-exposure depends on each aberration type of the projection opticalsystem itself or an illumination condition of an illumination opticalsystem as a matter of course. Such an image distortion became animportant error budget also for a stepper of a method (stationaryexposure method) with which a circuit pattern image on a reticle, whichis included in a projection field, is collectively transferred in a shotarea on a wafer in a state where a mask and the wafer are madestationary.

Accordingly, a projection optical system mounted in a conventionalstepper is optically designed so that the image distortion vector (thedirection and the amount of the deviation from the ideal position ofeach point image at an ideal lattice point), which occurs in eachlattice point image, becomes averagely small in an entire projectionfield. Lens elements and optical members are processed with highaccuracy, and assembled as the projection optical system by repeatingcomplicated and time-consuming tests in order to include the imagedistortion vector within a tolerable range when being designed.

To ease, however little, the difficulty in the manufacturing of such aprojection optical system, which requires high accuracy, the method foractually measuring the image distortion characteristic of an assembledprojection optical system, for inserting the optical correction plate(quartz plate), which is polished to partially deflect the principal raypassing through each point in a projection field, in a projectionoptical path so that the actually image distortion characteristicbecomes a minimum at each point in the projection field is disclosed,for example, by the Japanese Unexamined Patent Publication No. 8-203805(NC).

Additionally, the Japanese laid-open Publication No. 6-349702 (Nikon)discloses the method for adjusting aberration characteristics of aprojection optical system by rotating some of lens elements configuringthe projection optical system about an optical axis in order to improvethe image distortion characteristic occurring in a resist image on aphotosensitized substrate, which is transferred by scan-exposure.Furthermore, as disclosed by the Japanese laid-open Publications No.4-127514 (NC:Taniguchi) and No. 4-134813 (N:shiraishi), it is also knownthat a projection magnification, a distortion aberration, etc. areadjusted by infinitesimally moving some of lens elements configuring aprojection optical system.

However, there is a problem in that even if an aberration characteristicis adjusted by rotating some of lens elements configuring a projectionoptical system or by decentering or tilting an optical axis, this doesnot always guarantee that a satisfactory aberration characteristic(image distortion characteristic) can be obtained. Furthermore, it isdifficult to partially adjust and modify respective characteristics suchas a local image distortion, etc. within a projection area.

Therefore, if the optical correction plate disclosed by the JapaneseUnexamined Patent Publication No. 8-203805 (NC:Nikon) is manufacturedand inserted in a projection optical path, it is anticipated that alocal image distortion characteristic within an effective projectionarea can be easily improved. However, the conventional opticalcorrection plate explained in the Japanese Unexamined Patent PublicationNo. 8-203805 (NC:Nikon) is not assumed to be applied to the projectionoptical system used for scan-exposure. Accordingly, if an opticalcorrection plate is manufactured with the method disclosed in thispublication as it is, its design and manufacturing become extremelycomplicated. Especially, the accuracy for processing the shape of alocal surface of the optical correction plate with a wavelength order(order of nanometer to micrometer) becomes stricter.

SUMMARY OF THE INVENTION

The present invention was developed in the above described background. Afirst object of the present invention is to provide an exposure methodand apparatus which can accurately expose a substrate with a patternformed on a mask.

A second object of the present invention is to provide an exposuremethod and apparatus which can form a mask pattern image on a substratein a desired state.

A third object of the present invention is to provide an exposure methodand apparatus which comprises an optical correction element suitable fora scan-exposure method, and can easily reduce a projection aberrationoccurring at the time of scan-exposure.

A further object of the present invention is to provide an exposuremethod for easily reducing an image distortion error occurring whenbeing scan-exposed by using the projection optical system includingoptical correction elements suitable for a scan-exposure method.

A still further object of the present invention is to provide aprojection exposure apparatus including such optical correctionelements, and the method for manufacturing a circuit device by using theprojection exposure apparatus.

A still further object of the present invention is to provide an imageformation performance automatic measurement system for use in alithography device, which measures an image distortion error of aprojection optical system including an optical correction element yet tobe processed in a state of being mounted in a projection exposureapparatus of a scanning type, and can automatically simulate a processcondition such as a plane shape of an optical correction element to beprocessed and an installment condition (tilt, etc.) for the projectionoptical system based on the result of the measurement.

A still further object of the present invention is to easily self-testthe performance of a projection exposure apparatus periodically ordepending on need by using such an image formation performance automaticmeasurement system.

A still further object of the present invention is to immediately obtaina change in an image formation performance, which can possibly occurwhile a projection exposure apparatus is being used on a manufacturingline, especially, a change in a random image distortion error(aberration characteristic).

According to one aspect of the present invention, a pattern of a mask(R) is scan-exposed onto a substrate (W) by moving the mask(R) and thesubstrate (W) in a scanning direction in a state where the mask (reticleR) is arranged on an object plane side of a projection optical system(PL) having a predetermined image formation characteristic, thesubstrate (wafer W) is arranged on its image plane side, a partial imageof the mask (R) which is projected onto the image plane side isrestricted to within a projection area (EIA) having a predeterminedwidth in a one-dimensional scanning direction, and at least one opticalcorrection element (an image distortion correction plate G1, anastigmatism/coma correction plate G3, or an image plane curvaturecorrection plate G4), which is optically processed so that an averageaberration characteristic obtained by averaging the projectionaberrations at a plurality of image points existing in sequence in thescanning direction becomes a predetermined state at each of a pluralityof positions in a non-scanning direction intersecting the scanningdirection of the projection area (EIA), is arranged in an imageformation optical path by a projection optical system (PL).

According to the present invention of the above described configuration,it becomes possible to satisfactorily correct projection aberrationsinfluenced by the aberrations of both of an illumination optical systemand a projection optical system, especially, a dynamic distortioncharacteristic, an astigmatism characteristic, a coma characteristic,and an image plane curvature characteristic at the time ofscan-exposure, thereby accurately exposing a mask pattern onto asubstrate.

According to another aspect of the present invention, in an exposuremethod for exposing a substrate (W) by projecting a pattern of a mask(R) onto the substrate (W) through a projection optical system (PL), amask pattern image is projected through the projection optical system ina state where the mask (R) and the substrate (W) are arranged, and anastigmatism correction plate (G3) for correcting a random astigmatismcharacteristic of each image at a plurality of positions within aprojection area (EIA) of the projection optical system is arrangedbetween the mask (R) and the substrate (W) in order to expose thesubstrate.

According to the present invention, it becomes possible tosatisfactorily correct a random astigmatism characteristic within aprojection area, thereby accurately exposing a mask pattern onto asubstrate.

According to a further aspect of the present invention, in an exposuremethod for exposing a substrate (W) by projecting a pattern of a mask(R) onto the substrate (W) through a projection optical system (PL), amask pattern image is projected through a projection optical system in astate where the mask (R) and the substrate (W) are arranged, and a comacorrection plate (G3) for correcting a random coma characteristic ofeach image at a plurality of positions within a projection area (EIA) ofthe projection optical system (PL) is arranged between the mask (R) andthe substrate (W) in order to expose the substrate.

According to the present invention, it becomes possible tosatisfactorily correct a random coma characteristic within a projectionarea, thereby accurately exposing a mask pattern onto a substrate.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic showing the detailed configuration of the mainbody of a projection exposure apparatus;

FIG. 2 shows one example of a telecentric error of a projection opticalsystem, which is measured by an image detector;

FIG. 3 is a partial sectional view showing the state of anastigmatism/coma correction plate arranged on an image plane side of aprojection optical system, and an image plane curvature correctionplate;

FIG. 4 is a schematic explaining a difference of a numerical apertureaccording to an image height of image formation luminous flux (orillumination luminous flux) projected onto a projection image plane sidethrough a projection optical system;

FIG. 5 is a schematic showing the structure of a measurement sensor formeasuring an NA difference according to an image height of theillumination luminous flux, and its processing circuit;

FIG. 6A is a schematic illustratively showing first example of a lightsource image within an illumination optical system, which is measured bythe measurement sensor shown in FIG. 5;

FIG. 6B is a schematic illustratively showing second example of a lightsource image within an illumination optical system, which is measured bythe measurement sensor shown in FIG. 5;

FIG. 7 is a schematic explaining an optical path from a fly-eye lensconfiguring an illumination optical system to an illuminated plane, andan NA difference of an illumination light focusing on one point on theirradiated surface;

FIG. 8A is a schematic showing the arrangement of an illumination NAcorrection plate for correcting an NA difference according to an imageheight of an illumination light;

FIG. 8B is a top view showing the structure of the correction plateshown in FIG. 8A;

FIG. 9 is a schematic illustratively explaining the exchange and theadjustment mechanisms of aberration correction plates of respectivetypes installed in a projection exposure apparatus;

FIG. 10A is a schematic illustratively explaining first type of aprojection optical system to which the present invention is applied;

FIG. 10B is a schematic illustratively explaining second type of aprojection optical system to which the present invention is applied;

FIG. 10C is a schematic illustratively explaining third type of aprojection optical system to which the present invention is applied;

FIG. 11 is a schematic showing the array of shot areas on a wafer ontowhich a test reticle pattern is scanned and exposed at the time of testprinting, and the state of one shot area within the array;

FIG. 12 is a schematic explaining the state where respective projectionimages of a measurement mark pattern within one shot area, which istest-printed, are grouped and averaged;

FIG. 13 is a perspective view illustratively showing the entireappearance of a projection exposure apparatus preferable for practicingthe present invention;

FIG. 14 is a schematic illustratively exemplifying a distortioncharacteristic which occurs within the projection field of theprojection optical system shown in FIGS. 1 and 13;

FIG. 15 is a schematic explaining the averaging of the distortioncharacteristic (image distortion vector) by using a scan-exposuresystem;

FIG. 16A is a schematic explaining first typical example of an averageddynamic distortion characteristic;

FIG. 16B is a schematic explaining second typical example of an averageddynamic distortion characteristic;

FIG. 16C is a schematic explaining third typical example of an averageddynamic distortion characteristic;

FIG. 16D is a schematic explaining fourth typical example of an averageddynamic distortion characteristic;

FIG. 17A is a schematic explaining the case where a dynamic imagedistortion vector which occurs at random is corrected to be approximatedto a predetermined function (before correction);

FIG. 17B is a schematic explaining the case where a dynamic imagedistortion vector which occurs at random is corrected to be approximatedto a predetermined function (after correction);

FIG. 18 is a schematic explaining how to obtain a correction vector forcorrecting a dynamic image distortion vector;

FIG. 19 is a partially enlarged view explaining the correction of imageformation luminous flux by an image distortion correction plate;

FIG. 20 is an enlarged partially sectional view which exaggeratinglyshows the state where the surface of the image distortion correctionplate shown in FIG. 19 is locally polished;

FIG. 21 is a plan view illustratively exemplifying the distributionstate of locally polished areas on the image distortion correction platewhich is finally polished;

FIG. 22 is a schematic showing the simplified configuration of apolishing processor preferable for polishing the image distortioncorrection plate shown in FIG. 21;

FIG. 23 is a plan view showing the configuration of a support plate onwhich the image distortion correction plate shown in FIG. 21 is mounted;

FIG. 24 is a partially sectional view showing the state of the imagedistortion correction plate inserted in the optical path of theprojection optical system of the projection exposure apparatus alongwith the support plate shown in FIG. 23, and its holding structure;

FIG. 25 is a schematic showing the structure of an image detectormounted on the wafer stage of the projection exposure apparatus, and theconfiguration of its processing circuitry;

FIG. 26 is plan views showing the configuration of a test reticle onwhich measurement marks for measuring respective aberrationcharacteristic types are formed, and the state of a measurement patterngroup formed within one measurement mark area;

FIG. 27 is a schematic explaining the detection of the image of an L&Spattern on a test reticle, which is projected onto one location on aprojection image plane;

FIG. 28 is a chart exemplifying the waveform of the photoelectric signaloutput from the image detector;

FIG. 29 is a chart showing the waveform of the signal output from theimage detector and its differential signal;

FIG. 30 is a timing chart showing the relationship between themeasurement pulse of a laser interferometer for a wafer stage and thetrigger pulse of an excimer laser light source;

FIG. 31 is a circuit diagram exemplifying the modification of theprocessing circuit which digitally converts the photoelectric signalfrom the image detector and stores the converted signal; and

FIG. 32 is a schematic exaggeratingly exemplifying the case where bothsides of an image distortion correction plate are polished.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The entire configuration of a projection exposure apparatus which ispreferable for practicing the present invention is explained byreferring to FIG. 1. A projection exposure apparatus shown in FIG. 1 isintended to transfer the whole of a circuit pattern of a reticle inrespective shot areas on a wafer W with a step-and-scan method byrelatively scanning the reticle and the wafer W in a one-dimensionaldirection against a field of a projection optical system PL whileprojecting a partial image of the circuit pattern drawn on the reticleas a mask substrate onto the semiconductor wafer W as a photosensitizedsubstrate through the projection optical system PL. In FIG. 1, it isassumed that the optical axis direction of the projection optical systemPL is Z direction, the scanning direction of the reticle R on the planevertical to the optical axis of the projection optical system PL is Ydirection, and the direction vertical to the scanning direction of thereticle R is X direction.

In FIG. 1, after an ultraviolet pulse light output from an excimer laserlight source 1 passes through a tube 3 and is adjusted to be apredetermined peak intensity by a variable beam attenuator 7A, it ismodified to be a predetermined sectional shape by a beam modifier 7B.The sectional shape is set to be similar to the entire shape of anentrance of a first fly-eye lens system 7C for making the intensitydistribution of an illumination light even. Note that the excimer laserlight source 1 pulse-emits, representatively, a KrF excimer laser beamhaving a wavelength of 248 nm or an ArF excimer laser beam having awavelength of 193 nm.

Additionally, examples of an exposure apparatus which uses excimer laseras a light source are disclosed by the Japanese laid-open PublicationsNo. 57-198631 (IBM), No. 1-259533 (NC: Ichihara), No. 2-135723 (NC:Hazama), No. 2-294013 (NC: Uemura), etc., while examples of an exposureapparatus which uses an excimer laser light source for step-and-scanexposure are disclosed by the Japanese laid-open Publications No.2-229423, No. 6-132195, No. 7-142354, etc. Accordingly, also to theexposure apparatus shown in FIG. 1, the fundamental techniques disclosedby the above described publications can be applied as they are or bybeing partially modified.

An ultraviolet pulse light emitted from many point light sources, whichis generated on an exit side of the first fly-eye lens system 7C, entersa second fly-eye lens system 7G via a vibration mirror 7D for smoothinginterference fringes or a weak speckle occurring on an irradiated plane(a reticle plane or a wafer plane), a collective lens system 7E, anillumination NA correction plate 7F for adjusting the directionality(illumination NA difference) of a numerical aperture on the planeirradiated by an illumination light. The second fly-eye lens system 7Gconfigures a double fly-eye lens system together with the first fly-eyelens system 7C and the collective lens system 7E. The configurationwhere such a double fly-eye lens system and the vibration mirror 7B arecombined is disclosed in detail, for example, by the Japanese laid-openPublications No. 1-235289 (NC: Ichihara) and No. 7-142454 (NC: Ozawa).

On the exit side of the second fly-eye lens system 7G, a switch-typeillumination a diaphragm plate 7H for restricting the shape of a lightsource plane to an annular shape, a small circle, a large circle, etc.or for forming a four separated light source planes is arranged. Theultraviolet pulse light passing through the diaphragm plate 7H isreflected by a mirror 7J, and irradiates the aperture of an illuminationfield diaphragm (reticle blind) 7L by a collective lens 7K with anuniform intensity distribution.

Note that, however, interference fringes or a weak speckle with acontrast of several percent depending on the coherency of theultraviolet pulse light from the excimer laser light source 1 may besuperposed on the intensity distribution.

Accordingly, on the wafer plane, exposure amount unevenness may occurdue to the interference fringes or weak speckle. However, the exposureamount unevenness is smoothed by vibrating the vibration mirror 7D insynchronization with the moving of the reticle or the wafer W at thetime of scan-exposure and the oscillation of an ultraviolet pulse light,as disclosed by the above described patent publication No. 7-142354.

The ultraviolet pulse light which passes through the aperture of thereticle blind 7L in this way is irradiated on the reticle R via acollective lens system 7M, an illumination telecentric correction plate(a quartz parallel plate which can be tilted) 7N, a mirror 7P, and amain condenser lens system 7Q. At that time, an illumination areasimilar to the aperture of the reticle blind 7L is formed on the reticleR. In this preferred embodiment, the illumination area is defined to bea slit shape or a rectangular shape, which extends in the directionorthogonal to the moving direction of the reticle R at the time ofscan-exposure. If the width of the shading band in the periphery of acircuit pattern on the reticle is desired to be narrowed or if the scanmoving stroke of the reticle is desired to be reduced as short aspossible, it is desirable that the mechanism for changing the width ofthe scanning direction of the reticle blind during scan-exposure isarranged, for example, as recited in the Japanese laid-open PublicationNo. 4-196513.

The aperture of the reticle blind 7L is set to be conjugate to thereticle R by the collective lens system 7M and the condenser lens system7Q. Also this aperture is formed to be a slit shape or a =rectangularshape, which extends in the X direction. By such an aperture of thereticle blind 7L, part of the circuit pattern area on the reticle R isilluminated, and the image luminous flux from the illuminated part ofthe circuit pattern is reduced to one-fourth or one-fifth and projectedonto the wafer W through the projection lens system PL.

In this embodiment, it is assumed that the projection lens system PL isa telecentric system on both of the object plane (reticle R) side andthe image plane (wafer W) side, and has a circular projection field.Additionally, the projection lens system PL is assumed to be composed ofonly a dioptric element (lens element) in this embodiment. However, theprojection lens system PL may be a catadioptric system where a dioptricelement and a catoptric element are combined, as disclosed by theJapanese laid-open Publication No. 3-282527 (NC).

In a position close to the object plane of his projection lens systemPL, a telecentric unit lens system G2 which can infinitesimally move ortilt is arranged. By the movement of the lens system G2, themagnification (the aberration of isotropic distortion) or the aberrationof non-isotropic distortion such as a barrel-shaped, a spool-shaped, atrapezoid-shaped distortion, etc. of the projection lens system PL canbe adjusted finely. Additionally, in a position close to the image planeof the projection lens system PL, an astigmatism/coma aberrationcorrection plate G3 for reducing an astigmatism aberration or comaaberration, which may frequently occur in an area, which is close to theperiphery of a projection field, where an image height of a projectionimage is especially high, and for especially reducing a randomastigmatism or coma aberration.

In this embodiment, an image distortion correction plate G1 foreffectively reducing a random distortion component included in aprojection image formed on an effective image projection area(stipulated by the aperture portion of the reticle blind 7L) within acircular field, is arranged between the lens system G2 of the projectionlens system PL and the reticle R. This correction plate G1 is made bylocally polishing the surface of a quartz or fluorite parallel platehaving a thickness of approximately several millimeters, andinfinitesimally deflects the image luminous flux which passes throughthe polished portion.

For the respective optical components which configure the abovedescribed illumination or projection optical paths, a driving mechanism40 for switching or continually varying a beam attenuation filter of thevariable beam attenuator 7A, a driving system 41 for controlling thevibrations (deflection angle) of the vibration mirror 7B, a drivingmechanism 42 for moving a blind blade in order to continually vary theshape of the aperture of the reticle blind 7L, especially a slit width,and a driving mechanism 43 for infinitesimally moving the lens system G2within the projection lens system PL described above are arranged in thesystem according to this embodiment.

Additionally, in this embodiment, also a lens controller 44 forcorrecting an isotropic distortion aberration (projection magnification)by sealing a particular air chamber within the projection lens system PLfrom the open air, and applying a gas pressure within the sealedchamber, for example, in a range of approximately ±20 mmHg. This lenscontroller 44 also serves as a controlling system for the driving system43 of the lens system G2, and controls a magnification change byswitching between the driving of the lens system G2 and the pressurecontrol of the sealed chamber within the projection lens system PL, orby using both of them.

However, if the ArF excimer laser light source with a wavelength of 193nm is used as an illumination light, the mechanism forincreasing/decreasing the pressure within the particular air chamberwithin the projection lens system PL may be omitted. This is because theinsides of the illumination paths and the lens barrel of the lens systemPL are replaced by nitrogen or helium gas.

To part of a reticle stage 8 supporting the reticle R, a movable mirror48 for reflecting a measurement beam from a laser interferometer 46 formeasuring a move position or a move amount is installed. In FIG. 1, theinterferometer 46 is illustrated to be suitable for a measurement in thex direction (non-scanning direction). Actually, however, aninterferometer for measuring a position in the Y direction and aninterferometer for measuring the e direction (rotation direction) arearranged, and movable mirrors corresponding to the respectiveinterferometers are securely disposed to the reticle stage 8.Accordingly, in the explanation provided below, the measurements of theX, Y, and e directions are assumed to be individually made by the laserinterferometer 46 at the same time for the sake of convenience.

The positional information (or the speed information) of the reticlestage 8 (that is, the reticle R) measured by the interferometer 46 istransmitted to a stage controlling system 50. The stage controllingsystem 50 fundamentally controls a driving system (such as a linearmotor, a voice coil motor, a piezo motor, etc.) 52 so that thepositional information (or the speed information) output from theinterferometer 46 matches an instruction value (target position ortarget speed).

In the meantime, a table TB for supporting and flattering the wafer Wwith vacuum absorption is arranged on a wafer stage 14. This table TB isinfinitesimally moved in the Z direction (the optical axis direction ofthe projection optical system PL) and tilted relative to the X-Y planeby three actuators (piezo, voice coil, etc.) ZAC arranged on the waferstage 14. These actuators ZAC are driven by a driving system 56, and adriving instruction to the driving system 56 is issued from acontrolling system 58 of the wafer stage.

Although not shown in FIG. 1, a focus leveling sensor for detecting adeviation (focus error) or a tilt (leveling error) in the Z directionbetween the image plane of the projection optical system PL and thesurface of the wafer W is arranged in the neighborhood of the projectionoptical system PL, and the controlling system 58 controls the drivingsystem 56 in response to a focus error signal or a leveling error signalfrom that sensor. An example of such a focus/leveling detection systemis disclosed in detail by the Japanese laid-open Publication NO.7-201699 (NC: Okumura).

Additionally, to part of the table TB, a movable mirror 60 used tomeasure the coordinate position of the wafer W, which changes with themoving of the wafer stage 14 on the X-Y plane, is secured. The positionof the movable mirror 60 is measured by a laser interferometer 62. Here,the movable mirror 60 is arranged to measure the movement position (orspeed) of the stage 14 in the X direction. Actually, however, also themovable mirror for measuring a movement position in the Y direction isarranged, and a critical dimension measurement beam is irradiated fromthe laser interferometer also to the movable mirror for the Y directionin a similar manner.

Additionally, the laser interferometer 62 comprises a differentialinterferometer for measuring an infinitesimal rotation error (includingalso a yawing component), which can occur on the X-Y plane due to an X-Ymove of the wafer stage 14 or an infinitesimal move of the table TB, inreal time. The respectively measured positional information of the X, Y,and θ directions of the wafer W are transmitted to the wafer stagecontrolling system 58. This controlling system 58 outputs a drivingsignal to the driving system (such as three linear motors) 64 fordriving the wafer stage 14 in the X and the Y directions based on thepositional or speed information measured by the interferometer 62 and aninstruction value.

Furthermore, a synchronous controlling system 66 monitors the states ofthe respective positions and speeds of the reticle R and the wafer W,which are measured by the respective interferometers 46 and 62 in realtime, in order to make the control of the driving system 52, which isperformed by the reticle stage controlling system 50, and the control ofthe driving system 64, which is performed by the wafer stage controllingsystem 58, reciprocally function, especially when the reticle stage 8and the wafer stage 14 are synchronously moved at the time ofscan-exposure, and manages the reciprocal relationship therebetween tobe a predetermined one. The synchronous controlling system 66 iscontrolled by respective command and parameter types from a minicomputer32.

In this embodiment, an image detector KES for photoelectricallydetecting a test pattern image or an alignment mark image on the reticleR, which are projected through the projection optical system PL, issecured to part of the table TB. This image detector KES is attached sothat its surface is as high as the surface of the wafer W.

On the surface of the image detector KES, a shading plate is formed. Onthe shading plate, a multi-slit or a rectangular aperture (knife-edgeaperture) through which part of an image projected by the projectionoptical system PL passes is formed, and image luminous flux which passesthrough the slit or the aperture is detected as a quantity of light.

In this embodiment, the image formation performance of the projectionoptical system PL or the illumination characteristic of the illuminationoptical system can be measured by the image detector KES, and theoptical elements and mechanisms of the respective types shown in FIG. 1can be adjusted based on the measurement result. Examples of theconfiguration of the image detector and a measurement using the imagedetector are disclosed in detail by the Japanese laid-open PublicationsNo. 9-115820 (Nikon) and No. 9-153448 (Nikon).

Additionally, in the system configuration according to this embodimentshown in FIG. 1 , an alignment optical system ALG of an off-axis typefor optically detecting an alignment mark formed in each shot area onthe wafer W, or a reference mark formed on the surface of the imagedetector KES, is arranged very much close to the projection opticalsystem PL. This alignment optical system ALG irradiates anon-photosensitized illumination light (overall or spot illumination) toa resist layer on the wafer W through an objective lens, andphotoelectrically detects a light reflected from the alignment orreference mark through the objective lens.

The photoelectrically detected mark detection signal iswaveform-processed by a signal processing circuit 68 according to apredetermined algorithm, and the coordinate position (shot alignmentposition) of the wafer stage 14, such that the center of the markmatches the detection center (indication mark, a reference pixel on theimage plane, a reception slit, a spot light, etc.) within the alignmentoptical system ALG, or the positional deviation amount of the wafer markor the reference mark from the detection center is obtained incooperation with the interferometer 62. Thus obtained information of thealignment position or the position deviation amount is transmitted tothe minicomputer 32, and is used to align the position of the waferstage 14 or to set the start position of scan-exposure for each shotarea on the wafer W.

Next, the method for manufacturing the image distortion correction plateG1 as one characteristic configuration in this embodiment will bebriefly explained.

As described above, the correction plate G1 is configured to be a plateon which part of the surface of a quartz or fluorite parallel plate ispolished with the precision of a wavelength order, and a predeterminedinfinitesimal slope is formed on part of the surface, and is intended tochange an image distortion on an image plane by deflecting the principalray of local image luminous flux, which passes through the infinitesimalslope.

An example of the method for manufacturing this correction plate G1 orits operation is disclosed in detail by the Japanese laid-openpublication No. 8-203805 (Nikon).

In case of scan-exposure, an image distortion which statically occurs ateach of a plurality of images arranged in the move direction of thewafer W at the time of scan-exposure emerges as a dynamic imagedistortion which is averaged or accumulated within an effective exposurefield (exposure slit width). Accordingly, a random image distortionconsequently remains even if a static distortion characteristic iscorrected in case of scan-exposure.

Therefore, in this embodiment, close attention is paid not to the staticdistortion characteristic (distortion aberration characteristic) withinthe effective projection area EIA at the time of scan-exposure, but tothe dynamic distortion characteristic which occurs due to theaccumulation (averaging) in the scanning direction of the projectionarea EIA, and the image distortion correction plate G1 is polished sothat the dynamic distortion characteristic becomes almost “0” or thedistortion characteristic becomes regular by correcting the randomcomponent included in the dynamic distortion characteristic.

For the process of the image distortion correcting plate G1, theoperation for measuring an image distortion causing a dynamic distortioncharacteristic is required at first. There are two types of the methodof the measurement operation: the offline measurement by test printing(test exposure), and the onbody measurement using the image detector KESsecured onto the wafer table TB of the projection exposure apparatusshown in FIG. 1.

The method of the test exposure is intended to obtain a static imagedistortion at each point within a circular field or at each point withinthe effective projection area EIA of the projection optical system PL bystatically exposing a test mark formed at an ideal lattice point on atest reticle onto a wafer W through the projection optical system PL, byconveying the exposed wafer W to a measurement device different from theprojection exposure apparatus after developing the wafer W, and bymeasuring the coordinate position or the position deviation amount ofthe printed test mark.

In the meantime, the method using the image detector KES is intended toobtain a static image distortion vector by moving the wafer stage 14 inthe X and the Y directions in order to scan an image with the knife-edgeof the image detector KES while projecting the image of a pattern of atest mark (a line and space pattern having a cycle in the X direction, aline and space pattern having a cycle in the Y direction, a RANPASU markor a vernier mark used to examine a resolution or an overlappingaccuracy, etc.) formed at each ideal lattice point on a test reticle ,and by analyzing the waveform of the photoelectric signal output fromthe image detector KES at that time.

After the static image distortion vector is obtained, a dynamicdistortion characteristic is obtained by averaging each image distortionin the scanning direction (Y direction) within the rectangular effectiveprojection area EIA with the use of a computer (a computer, aworkstation, etc.). Thereafter, the portion of the surface correspondingto the image distortion correction plate G1 is polished incorrespondence with the position in the non-scanning direction (Xdirection) based on the obtained dynamic distortion characteristic.

As described above, the polished image distortion correction plate G1 isrelocated in the initial position within the projection optical path,that is, the position located when the distortion characteristic ismeasured before being polished, and the measurement operation of thedistortion characteristic using a test reticle is again performed toexamine the dynamic distortion characteristic.

However, the distortion component must be reduced almost to “0” by theadjustment of the tilt of the image distortion correction plate G1, theup-and-down movement and the infinitesimal tilt of the lens element G2or the subtle change of the magnification by pressure control.Therefore, it is examined how much a random distortion component isincluded in the dynamic distortion characteristic re-measured after theadjustment. If the random component is within a standard value, thesequence of the manufacturing process of the image distortion correctionplate G1 is terminated.

In the meantime, if the random component in the dynamic distortioncharacteristic is not within the standard value, the image distortioncorrection plate G1 is again polished based on the re-measureddistortion error data depending on need.

Explained next is the optical condition of the illumination opticalsystem of the projection exposure system, which must be considered whena distortion characteristic is measured in this embodiment. As explainedearlier by referring to FIG. 1, the illumination optical system of theprojection exposure apparatus of this type is normally configured as aKohler's illumination system which images a plane light source image(actually a set of 5 to 10 thousand luminance points) formed on the exitside of the second fly-eye lens 7G at an entrance pupil or an exit pupilof the projection optical system PL. With this system, an evenilluminance distribution of approximately ±1 percent is respectivelyobtained at the position of the blind 7L as the first irradiated plane,the position of the pattern plane of the reticle R as the secondilluminated plane, and the position on the image plane (wafer plane) ofthe projection optical system PL as the third irradiated plane if nocontrast of the interference fringes (or speckle) caused by thecoherence of an excimer laser beam is assumed to exist.

However, with the recent improvement of the density and the minutenessof a semiconductor device, problems have arisen not only in the evennessof the illuminance distribution on an irradiated plane but also in thedeviation from a telecentric condition of an illumination lightirradiated on the irradiated plane (especially on the wafer plane), thatis, a telecentric error. Note that, however, this telecentric error isconstrued as including also a telecentric error possessed by theprojection optical system PL itself.

Especially, in recent years, the respective types of an illumination σdiaphragm plate (hereinafter referred to as a spatial filter) 7H such asan annular aperture, a 4-aperture, a small circular aperture, a largecircular aperture, etc. are arranged to be exchangeable on the exit sideof the second fly-eye lens 7G as shown in FIG. 1, and the shape of theillumination light source plane is changed according to the pattern onthe reticle R.

In this case, the telecentric correction plate 7H may be inserted in thepotical path in the neighborhood of the condenser lens system shown inFIG. 1, wherein the telecentric correction plate 7H is polished with amethod similar to the method for manufacturing the image distortioncorrection plate G1 so as to correct a telecentric error of theillumination light at each point on the irradiated plane, and whereinthe telecentric error of the illumination light reaching the wafer W ismeasured at the each point of the irradiated plane in a state where thespatial filter 7H is not inserted in the optical path or in a statewhere the large circular aperture of the spatial filter 7H is insertedin the optical path. Or, in this case, an aspheric process, such thatthe measured telecentric error is corrected, may be performed for aparticular lens element included in the condenser lens system 7K, 7Q,etc. shown in FIG. 1.

Accordingly, it becomes necessary to accurately measure the telecentricerror of an illumination light on the image plane side of the projectionoptical system PL. For that measurement, the above described imagedetector KES and test reticle TR can be used as they are. To obtain thetelecentric error, the X-Y coordinate position of a projection image isrepeatedly measured by scanning the projection image of a line and space(L&S) pattern on the test reticle TR with the rectangular aperture ofthe image detector KES while changing the position of the wafer table TBin the Z direction by a predetermined amount (such as 0.5 μm) based onthe detection result of a focus detection system of an oblique incidentlight type, so that the change in the X-Y coordinate position of one L&Spattern image according to the change of the position in the Zdirection, that is, the direction and the amount of the tilt of theprincipal ray of the L&S pattern image to the Z axis are measured.

By making such a telecentric error (a tilt error of an image formationprincipal ray) measurement for each projection image of the L&S patternarranged at each ideal lattice point on the test reticle TR, thetelecentric error distribution within the projection image plane or theeffective projection area EIA can be known, for example, as FIG. 2. FIG.2 exemplifies the exaggerated distribution of a local telecentric erroroccurring within the effective area EIA. Black points in this figurerepresent ideal lattice points or points conforming thereto, and asegment extending from each of the black points represents a telecentricerror vector (direction and magnitude) Δθt(i,j).

This telecentric error vector Δθt(i,j) represents how much the principalray at a projection image point shifts in the X and the Y directions perdistance of 1000 μm in the Z direction as an example. The overalltendency of the vector map shown in FIG. 2 exhibits the coexistence of acomponent which is similar to a distortion characteristic and can befunction-approximated and a random component.

Accordingly, by measuring a telecentric error vector map like the oneshown in FIG. 2, the coordinate position within the projection field IFwhere a telecentric error to be modified (corrected) occurs isdetermined, and the correction amount of the of a principal ray at thedetermined coordinate position is calculated, and the infinitesimalslope of a wavelength order may be formed by locally polishing thesurface of the telecentric correction plate 7N (or lens element) basedon the result of the calculation.

Additionally, it is desirable to simulate the polished state of thetelecentric correction plate 7N by measuring the telecentric errorcharacteristic of an illumination light with the image detector KES, toperform an actual polishing process based on the result of thesimulation, and to perform the polishing process (modificationpolishing) again for the telecentric correction plate 7N inconsideration of the result of observing and measuring the state of theresist image by using an optical or an electric microscope when testprinting (scan-exposure) is performed with the processed telecentriccorrection plate 7N inserted.

As described above, the method for performing a polishing process basedon both of the result of photoelectric detection of a spatial intensitydistribution of a projection image, and a measurement result of thequality of an image which is actually etched on a resist layer by testprinting can be applied also to the manufacturing of the imagedistortion correction plate G1 as well as the telecentric correctionplate 7N, thereby maximizing the projection performance when an actualdevice pattern is scan-exposed onto the wafer W.

Additionally, the telecentric correction plate 7N can collectivelycorrect a telecentric error (offset amount) which equally occurs at eachpoint within the projection field if this plate is arranged to betiltable in a direction arbitrary to the plane vertical to the opticalaxis AX of the illumination system, similar to the image distortioncorrection plate G1 described earlier.

In the meantime, with the measurement of an L&S pattern projectionimage, which uses the image detector KES, an image plane astigmatism orcoma aberration occurring at each point within the projection field IFor within the rectangular projection area EIA, an image plane curvature,etc. can be measured. Accordingly, also the astigmatism/coma correctionplate G3 to be provided at the bottom of the projection optical systemPL, which is shown in FIG. 1, is polished so that the dynamic aberrationcharacteristic is reduced to “0” by averaging the aberration mount atthe time of scan-exposure, or a random component in the dynamicaberration characteristic is corrected, or the aberration amount isreduced to “0” in a static state based on the astigmatism/comaaberration amount measured at each point within the projection field IFor the rectangular projection area EIA, similar to the image distortioncorrection plate G1, the astigmatism/coma correction plate G3 isinserted in the bottom of the projection optical system PL after beingpolished.

Furthermore, although omitted in FIG. 1, the image plane curvaturecorrection plate (quartz plate) G4 having the plane shape for correctingthe curvature of a projection image plane is attached to the bottom ofthe projection optical system PL in parallel with the astigmatism/comacorrection plate G3. FIG. 3 is a partial sectional view showing thebottom of the projection optical system PL, and the state where a lenselement Ga closest to the projection image plane PF3 is secured withinthe lens barrel of the projection optical system PL through aring-shaped metal support 175, and the state where the astigmatism/comacorrection plate G3 and the image plane curvature correction plate G4are secured between the lens element Ga and the image plane PF3 withinthe lens the lens barrel with a ring-shaped metal support 176.

With the scan-exposure method, since a static image plane curvaturecharacteristic is added and averaged in a scanning direction, there is apossibility that a non-linear (random) image plane curvature error,which cannot be completely modified only by correcting an image tilt andan image plane curvature with the replacement of a lens element like astatic exposure method, remains.

Accordingly, in this embodiment, an image plane curvature correctionplate is processed to accurately correct a non-linear (random) imageplane curvature error in consideration of a dynamic image planecurvature characteristic.

Here, it is assumed that the image plane PF3 is a best focus plane whichis optically conjugate to the pattern plane of the reticle R, and aprimary ray ML′(i,j) of the image formation luminous flux LB′(i,j),which converges at an image point ISP2′, is parallel to the optical axisAX between the lens element Ga and the image plane PF3. At this time,the numerical aperture NAw of the image formation luminous flux LB′(i,j)is larger by an inverse number of the projection magnification (¼, ⅕,etc.) in comparison with the numerical aperture NAr on the reticle side,and is approximately 0.5 to 0.7.

Therefore, the spread area of the image luminous flux LB′(ij) whenpassing through the astigmatism/coma correction plate G3 and the imageplane curvature correction plate G4 becomes much larger than the imagedistortion correction plate G1 on the reticle side. Accordingly, theoverlapping between the image formation light which generates anotherimage point positioned in the neighborhood of the image point ISP2′ andthe image formation luminous flux LB′(i,j) on the astigmatism/comacorrection plate G3 cannot be avoided.

However, the polishing of the surface of the astigmatism/coma correctionplate G3 is not required to be taken into account for the entire surfaceof the astigmatism/coma correction plate G3, in consideration of thefact that also the aberration characteristic in the width direction(scanning direction) within the rectangular projection area EIA isaveraged by scan-exposure, and may be performed for a local area inconsideration of the averaging at the time of scan-exposure. Therefore,the stitching of a polished surface when polishing the astigmatism/comacorrection plate G3 can be relatively performed with ease.

In the meantime, the image plane curvature is determined by measuringthe best focus position (Z position) of each image of L&S patternsformed on the test reticle TR, which is projected under a certainillumination condition, with the off-line method by test printing andthe image detector KES, and by obtaining an approximate plane (a curvedsurface) on which the measured best focus position at each point isapproximated with a least square, etc.

In this case, the detection of a projected image with the image detectorKES is performed by changing the Z position of the table TB whilemeasuring the position of the height position of the surface of theshading plate of the image detector KES with a focus detection systemsuch as an oblique incident light method, etc., and the Z position ofthe table TB such that also the contrast (the peak value of adifferential waveform, a level of a bottom value) of the L&S patternprojection image becomes the highest is measured as the best focusposition.

If the flatness of the approximate plane of the projection image planethus determined is not within an allowable range at least in therectangular projection area EIA at the time of scan-exposure, thepolishing process such that an image plane curvature is modified bytaking out the image plane curvature correction plate G4 from theprojection optical system PL is performed. In this case, the image planecurvature correction plate G4 is normally manufactured to correct thetendency of the entire image plane curvature within the projection fieldby entirely polishing its one side with a positive curvature, and theother with almost a same negative curvature. As a result, the projectionimage plane by a projection optical system can be made entirely andlocally even, whereby a good effect of significantly improving a DOF(Depth Of Focus) can be promised.

If there is a portion where the image plane curvature is locally largewithin the projection field (with the rectangular projection area EIA),it is also possible to correct that portion by locally performingadditional polishing. Additionally, it is desirable to measure a profileof an actual resist image printed by test exposure and to consider alsothe result of that measurement not only depending on a photoelectricmeasurement result of a projection image by, which is obtained by theimage detector KES, also when the above described astigmatism/comacorrection plate G3, the image plane curvature correction plate G4 aremanufactured.

Next, other illumination condition which must be considered when theabove described distortion characteristic, astigmatism/coma aberration,image plane curvature, etc. are measured will be explained. As describedearlier, an even illuminance distribution of approximately ±1 percentcan be obtained on an irradiated plane of the position of the blind 7L,the position of the pattern plane on the reticle R (test reticle TR),the position of the image plane (wafer plane) of the projection opticalsystem PL, etc. by the operations of the first fly-eye lens 7C and thesecond fly-eye lens 7G, which are shown in FIG. 1.

However, it is also proved that the irradiation state of an illuminationlight has not only a problem in the evenness of an illuminancedistribution on an irradiated plane, but also a problem in the localdegradation of an overall image formation performance including aresolution, a distortion error, respective aberration types, etc. due tothe phenomenon that the numerical aperture (NA) of the illuminationlight partially differs according to the position on the irradiatedplane, that is, an occurrence of an NA difference (unevenness within anillumination angle) according to an image height which is the distancefrom the optical axis AX. This phenomenon is caused not only by a σvalue change depending on the image height position of the illuminationsystem, but also by the respective aberration types of the illuminationoptical system from the second fly-eye lens 7G to the reticle R shown inFIG. 1, an arrangement error when a plurality of optical componentsconfiguring the illumination optical system are assembled andmanufactured, or an angle characteristic of a thin film for preventing areflection, which is coated on the respective optical components, etc.

Additionally, such an NA difference of the illumination light accordingto the image height is a phenomenon which can possibly occur due to anaberration of the projection optical system PL by itself. After all, asexaggeratedly shown in FIG. 4, for example, numerical apertures NAa,NAb, and NAc of image formation luminous flux LBa, LBb, and LBc forforming respective three image points ISPa, ISPb, and ISPc on theprojection image plane PF3 differ depending on the image height position±ΔHx.

FIG. 4 shows the state where an object point (ideal lattice point) GPbat a position on the optical axis AX on the reticle R, an object pointGPc apart from the object point GPb by a distance M·ΔHx in a positivedirection (axis in a non-scanning direction) along the X axis, and anobject point GPa apart from the object point GPb by the distance M·ΔHxin a negative direction of the X axis are respectively imaged andprojected as image points ISPa, ISPb, and ISPc through a bilaterallytelecentric projection optical system PL at a reduction magnification1/M (M is on the order of 2 to 10).

At this time, the reticle R is irradiated with an almost even intensitydistribution by an illumination light ILB which is adjusted to be apredetermined numerical aperture and a predetermined σ value, and theimage formation luminous flux LBa, LBb, and LBc, which proceed to theimage plane PF3 side without being shaded by the pupil (diaphragmaperture) Ep of the projection optical system, among the lights enteringfrom the respective object points the projection optical system PL viathe image distortion correction plate G1, contribute to the imageformation of the respective image points.

Furthermore, in FIG. 4, partial luminous flux indicated by broken linesat the left side of the respective image luminous flux LBa and LBcrepresent portions which are lost as or attenuated as unevenness withinan illumination angle from the original aperture state. If an NAdifference according to the image height position as described above, agravity center line, which is determined by the center of gravity oflight quantity on each of the sectional planes of the image formationluminous flux LBa and LBc, becomes the one tilting from the principalray on the image plane PF3, although each of the principal rays of theimage formation luminous flux LBa at the image height+ΔHx, and the imageformation luminous flux at the image height−ΔHx passes through thecentral point (optical axis AX) of the pupil Ep.

Considered will be the case where an L&S pattern almost at a resolutionlimit, which is positioned, for example, in the center of theillumination area on the reticle R, that is, in the neighborhood of theoptical axis AX of the projection optical system PL, and an L&S patternalmost at a resolution limit, which is positioned at the periphery ofthe illumination area apart from the optical axis AX, are projected andexposed in the state where there is such an NA difference according tothe image height of the illumination light.

In this case, even if the intensity distributions of the illuminationlight irradiating the respective L&S patterns at the two positions areidentical, an effective NA of the illumination light for the L&S patternin the neighborhood of the optical axis AX is larger (smaller dependingon a case) than the illumination light for the L&S pattern apart fromthe optical axis AX. Therefore, a difference exists between theresolutions of the L&S patterns in the neighborhood and the periphery ofthe optical axis, which are finally transferred onto the wafer W, whichposes a problem such that the contrast or the line width of atransferred image may differ depending on the position on the imageplane although the L&S patterns have the same line width and pitch.

Additionally, the NA difference of the illumination light causes aproblem such that the line widths or duties of the projection images oftwo L&S patterns may be infinitesimally changed according to a pitchdirection, when the two L&S patterns of a same design with differentpitch directions are closely arranged on the reticle.

Although there is no effective NA difference between the center of anillumination area and its periphery, there may arise a problem such thatthe whole of the illumination luminous flux irradiated on the reticle R(or the wafer W) slightly tilts not at an angle symmetrical with respectto the optical axis AX, but in a certain direction. However, itsadjustment can be made by infinitesimally moving the positions of thesecond fly-eye lens 7G and the other optical elements within theillumination optical system in the X, Y, Z, or θ direction in that case.

The above described NA difference according to the image height of anillumination light naturally becomes a problem also when the abovedescribed distortion characteristic is measured, when the telecentricerror map shown in FIG. 2 is measured, or when the astigmatism/comaaberration and the image plane curvature are measured, and an error isincluded in measured static image distortion, telecentric error, etc.

Therefore, it is desirable that the NA difference according to the imageheight of an illumination light irradiated on the reticle R is adjustedwhen a distortion is measured at the time of manufacturing the imagedistortion correction plate G1, when a telecentric error is measured,when an astigmatism/coma aberration is measured, or when image planecurvature is measured, to say nothing of when a wafer is exposed on adevice manufacturing line. Arranged for such an adjustment is the platefor correcting an illumination NA difference (hereinafter referred to asan illumination NA correction plate) 7F, which is positioned on theincidence plane side of the second fly-eye lens 7G shown in FIG. 1.

In the meantime, the image detector KES explained earlier is intended todetect a quantity of light within a rectangular aperture on a projectionimage plane, and cannot detect the quantity by making a distinctionbetween the illuminance of an illumination light on a projection imageplane and the NA difference according to the image height of theillumination light. Meanwhile, since the resist layer on the wafer W isphotosensitized to the NA difference according to the image height of anillumination light and to an illuminance change, a definite distinctionemerges in the image formation characteristic (resist profile) of thepattern image projected onto the resist layer.

Accordingly, in this embodiment, an illumination NA measurement sensor200, which can automatically measure the NA difference according to theimage height of an illumination light at arbitrary timing while theapparatus is running, is arranged, for example, to beattachable/detachable onto/from the wafer table TB in FIG. 1 via a metalfixture Acm as shown in FIG. 5. FIG. 5 is an enlarged view showing thepartial structure of the table TB to which the illumination NAmeasurement sensor 200 is attached, and the bottom of the projectionoptical system PL. On the top of the sensor 200, a shading plate 201 onwhich a shading layer of chrome, etc. is formed on the entire surface ofa quartz plate is formed is arranged, and a pin hole 202 having adiameter which is determined based on a wavelength λ of an illuminationlight, the numerical aperture NAw on the image side of the projectionoptical system PL, etc. is arranged in a portion of the shading layer.

Under the pin hole 202 of the shading plate 201, a lens element 203 fortransforming an illumination light passing through the pin hole 202 intoparallel luminous flux, that is, a Fourier transform lens is arranged.On the Fourier transform plane implemented by the lens element 203, aCCD 204 as a two-dimensional imaging element is arranged. These shadingplate 201, lens element 203, and CCD 204 are collectively included in acase 205 of the sensor 200. The image signal from the CCD 204 istransmitted to a display 212 via a signal cable 206, an image processingcircuit 210, and a video signal mixer circuit 211. On the display 212, alight source image SSi which is formed in the pupil Ep is displayed.Note that the image processing circuit 210 comprises the software fordetecting the optical intensity distribution of the light source imageSSi in correspondence with the arrangement of the lens elements of thesecond fly-eye lens 7G, and for analyzing a portion which is especiallyuneven in the intensity distribution, and has a capability fortransmitting the result of the analysis to the main control system(minicomputer) 32 in FIG. 1.

In the above described configuration of the sensor 200, the surface ofthe shading plate 201 of the sensor 200 is located at the Z positionmatching the projection image plane PF3 of the projection optical systemPL, or the Z position accompanying a predetermined offset from theprojection image plane PF 3 by the focus detection system and theactuator ZAC in a predetermined leveling state, when the NA differenceof an illumination light is measured. Additionally, the XY stage 14 isdriven by the driving system 64 so that the pin hole 202 is located atarbitrary X, Y position within the projection field IF or therectangular projection area EIA of the projection optical system PL.

When a measurement is made, a reticle on which no patter is drawn ismounted on the reticle stage 8, the reticle is evenly illuminated by anillumination light ILB, and the pin hole 202 is located at the imageheight position to be measured within the projection field If or therectangular projection area EIA. Because the illumination light ILB is apulse light at that time, the illumination light which passes throughthe pin hole 202 is accumulated and photoelectrically detected while theillumination light ILB is irradiated with a predetermined number ofpulses if the CCD 204 is arranged as a charge storage type.

Since the imaging plane of the CCD 204 is the Fourier transform plane,the CCD 204 comes to image the intensity distribution of the lightsource image SSi formed in the pupil Ep of the projection optical systemPL. However, the light source image SSi formed in the pupil EP issimilar to the shape of the portion which has passed through theaperture of the spatial filter 7H among innumerable luminance point setplanes formed on the exit plane side of the second fly-eye lens 7G inFIG. 1.

Since this embodiment assumes the apparatus for performing scan-exposurein a width direction (Y direction) of the rectangular projection areaEIA, also an influence by the illumination NA difference of the qualityof a pattern image transferred onto the wafer W is an average of theillumination NA difference in the size of the width direction of theprojection area EIA. Accordingly, it is desirable to obtain a dynamicillumination NA difference by partitioning the projection area EIA intoa plurality of areas at predetermined intervals in the non-scanningdirection (X direction), and by averaging the static illumination NAdifference in the scanning direction for each of the partitioned areas,in a similar manner as in the case of the distortion measurement.

Therefore, the measurement of the static illumination NA difference willbe explained by referring to FIGS. 6(A) and 6(B). FIGS. 6(A) and 6(B)illustratively show the examples of the light source image SSi, whichare respectively displayed on the display 212 when the pin hole 202 islocated at different positions within the projection area EIA. On thescreen of the display 212, a cursor line representing an array 7G′(lightsource image SSi) of the lens element on the exit side of the secondfly-eye lens 7G, and scales SCLx and SCLy which represent the positionsin the X and the Y directions are displayed at the same time.

In FIGS. 6(A) and 6(B), the array 7G′ on the exit plane side of thesecond fly-eye lens 7G is modified to be almost a square as a whole, andthe sectional shape of each lens element is a rectangle which is almostsimilar to the projection area EIA. That is, since the incidence planeside of each lens element is conjugate to the irradiated plane (blindplane, reticle plane, or projection image plane), the size of thesectional shape in the scanning direction (Y direction) is smaller thanthat in the non-scanning direction (X direction) in order to efficientlyirradiate the projection area EIA on the irradiated plane.

In case of FIG. 6(A), each of the intensities of an area KLa at theupper left corner, an area KLb in the top row, and an area KLc at thelower right corner within the array 7G′ is lower than its peripheralintensity and a telerable value. Meanwhile, FIG. 6(B) shows an examplewhere each of the intensities of an area KLd at the upper right cornerand an area KLe at the lower right corner within the array 7G′ is lowerthan its peripheral intensity and a telerable value.

As described above, since the intensity distribution of the light sourceimage SSi formed in the pupil Ep of the projection optical system PLvaries according to the position within the projection field of the pinhole 202, that is, the image height, the quality of a projected image ofthe pattern formed on the reticle R (or TR) may be sometimesdeteriorated. For example, if the center of gravity of the entiredistribution of the light source image SSi (array 7G′) is decenteredfrom the coordinate origin (optical axis AX)in a lower left direction asshown in FIG. 6(A), the image formation luminous flux of the patternprojected at the image height position becomes the one deteriorated fromthe telecentric state. If a comparison is made between FIGS. 6(A) and6(B), an NA of illumination luminous flux on the projection image planePF3 is smaller as a whole in FIG. 6(A).

Note that the shape of the light source image SSi when the wafer W isactually scan-exposed is set by the aperture shape of the spatial filter7H which is arranged on the exit side of the second fly-eye lens 7G.Therefore, the shape of the light source image SSi becomes the apertureshape (circular, annular, 4-aperture, etc.) in the square array 7G′shown in FIG. 6(A) or 6(B), which is restricted by the spatial filter7H.

To average such an illumination NA difference according to the imageheight within the projection field, a plurality of measurement points ina matrix state are set within the rectangular projection area EIA, theimage signal from the CCD 204 is observed on the display 212 each timethe pin hole 202 is located at each of the measurement points, and anuneven area within the intensity distribution of the light source imageSSi (array 7G′) is analyzed by the image processing circuit 210, and thestatic illumination NA characteristic (the vector representing thedirectionality of an NA and its degree) at each of the measurementpoints is sequentially stored based on the result of the analysis.

Thereafter, a dynamic illumination NA characteristic is calculated byaveraging the illumination NA characteristic at several measurementpoints arranged in the scanning direction among the static illuminationNA characteristic at the respective measurement points. This dynamicillumination NA characteristic is obtained at predetermined intervals inthe non-scanning direction of the rectangular projection area EIA, andthe illumination NA difference according to the image height is obtainedparticularly in the non-scanning direction by making a comparisonbetween the dynamic illumination NA characteristics.

Then, the illumination NA correction plate 7F which is arranged on theincidence plane side of the second fly-eye lens 7G in FIG. 1 isprocessed based on the dynamic illumination NA characteristic thusobtained, and a correction is made to reduce the difference between thedynamic illumination NAs in the non-scanning direction almost to “0”.Since the rectangular projection area EIA is set along the diameterextending in the non-scanning direction within the circular projectionfield IF of the projection optical system PL, the dynamic illuminationNA is the one according to the image height from the optical axis AX.

Accordingly, to correct the dynamic illumination NA difference in thenon-scanning direction, the illumination NA correction plate 7F may bemanufactured to endow the illumination σ value at each image height inthe non-scanning direction with an offset. As a method for changing theillumination σ value depending on the image height, for example, a beamattenuating part for changing the size or the intensity of theillumination luminous flux entering each lens element or for decenteringthe intensity distribution for each lens element (rod lens) in theperiphery on the incidence plane side of the second fly-eye lens 7G maybe locally formed on a transparent (quarts) plate.

Therefore, the state of the illumination light on the irradiated planwill be briefly explained by referring to FIG. 7. FIG. 7 illustrativelyshows the system from the second fly-eye lens 7G to the irradiated planePF1, which is shown in FIG. 1. A collective lens system 180 represents asynthetic system of the mirror 7J, the collective lenses 7K and 7M, themirror 7P, and the condenser lens system 7Q, which are shown in FIG. 1.Accordingly, the irradiated plane PF1 is assumed to be the pattern planeof the reticle R, which is the second irradiated plane, for ease ofexplanation. However, the illumination NA difference to be actuallyevaluated is obtained by the projection image plane PF3 on the wafer W(or the shading plate 201 of the measurement sensor 200) side, which isthe third irradiated plane including the projection optical system PL.

In FIG. 7, the second fly-eye lens 7G is a bundle of a plurality ofsquare-pillar-shaped rod lenses, and the illumination luminous flux ILBincident on the incidence plane PF0 which is conjugate to the irradiatedplane PF1 is split by each of the rod lenses and collected as aplurality of point light source images (collective points) on the exitplane Ep′ side. Here, the light source images formed on the exit planeEp′ side of the rod lenses apart from the optical axis AX within thesecond fly-eye lens 7G are respectively assumed to be QPa and QPb.

However, since the first fly-eye lens 7C is arranged in this embodimentas explained earlier by referring to FIG. 1, the light source imageformed on the exit plane Ep′ side of one rod lens of the second fly-eyelens is an aggregate of the plurality of point light source imagesformed on the exit side of the first fly-eye lens 7C. Viewing from theirradiated plane PF1, the exit plane Ep′ of the second fly-eye lens 7Gis a Fourier transform plane (pupil plane), and the split light whichdiverges and proceeds from each of the rod lenses of the second fly-eyelens 7G is transformed into almost parallel luminous flux, andintegrated on the irradiated plane PF1. In this way, the intensitydistribution of the illumination light on the irradiated plane PF1 ismade even.

However, observing the state of the illumination luminous fluxirradiated at a peripheral irradiated point ISP1 apart from the opticalaxis AX on the irradiated plane PF1 in the non-scanning direction (Xdirection), the numerical aperture of the illumination luminous fluxconverged at the point ISP1 becomes smaller relatively in the Xdirection due to an intensity-attenuated portion DK1 within the luminousflux, as shown in the perspective view in the lower left of FIG. 7.Notice that ML1 represents a principal ray which passes through thecentral point of the pupil of the projection optical system PL andreaches the irradiated point ISP1 in this figure.

As described above, the illumination luminous flux including theattenuated (or intensified) portion like the portion DK1 can possiblyoccur if the intensity of the light source image QPa formed by the rodlens positioned at the left end of the second fly-eye lens 7 isextremely low (or extremely high), or if the intensity of the lightsource image QPb formed by the rod lens positioned at the right end ofthe second fly-eye lens 7G is extremely high (or extremely low).

Accordingly, for example, as shown in FIG. 8(A), a thin film filter unitSGa or SGb through which the illumination luminous flux having a widthDFx, which enters the rod lens at the left or right end of the secondfly-eye lens 7G, is entirely or partially beam-attenuated is formed onthe illumination NA correction plate 7F as a shading unit. FIG. 8(A) isa schematic showing the positional relationship between the secondfly-eye lens 7G and the illumination NA correction plate 7F, which isenlarged on the X-Z plane, while FIG. 8(B) is a schematic showing thepositional relationship in terms of a plane between filter units SGa andSGb formed on the illumination NA correction plate 7F, and a rod lens (arectangular section) array of the second fly-eye lens 7G.

As shown in FIG. 8(B), the section of each of the rod lenses of thesecond fly-eye lens 7G is a rectangle extending in the non-scanningdirection (X direction), and the filter units SGa and SGb areindividually arranged for each of the rod lenses existing in sequence inthe Y direction at both ends of each rod lens array in the X direction.Since the dynamic illumination NA difference, especially, in thenon-scanning direction is corrected in this embodiment, the filter unitsSGa and SGb are set by paying close attention to both ends of thesequence of rod lenses arranged mainly in the X direction also for therod lens arrays of the second fly-eye lens 7G.

Accordingly, only either of the filter units SGa and SGb may bearranged, and the shape of the filter unit SGa or SGb may be madeidentical for the rod lenses staying in the Y direction. Here, however,the shapes and the locations of the filter units SGa and SGb are set tobe different little by little according to the positions of the rodlenses arranged in the Y direction, and the dynamic illumination NAdifference becomes small not only in the non-scanning direction but alsoin the scanning direction (Y direction).

Also when the illumination NA correction plate 7F is made as describedabove, the dynamic illumination NA characteristic is measured with themeasurement sensor 200 of FIG. 5 in a state where a completelytransparent plate (quartz) which becomes a preform of the illuminationNA correction plate 7F is arranged on the incidence plane side of thesecond fly-eye lens 7G as shown in FIG. 1, and the reticle R isexchanged for a reticle on which no pattern is drawn, in a similarmanner as in the above described manufacturing of the image distortioncorrection plate G1. Then, the filter units SGa and SGb which becomebeam-attenuating parts, etc. may be formed on the transparent plate (orits equivalence) which is removed from an exposure apparatus based onthe result of the measurement.

As a matter of course, it is desirable to examine whether or not acorrection of a dynamic illumination NA difference according to an imageheight is satisfactorily made by re-measuring the dynamic illuminationNA characteristic with the measurement sensor 200 of FIG. 5 after amanufactured illumination NA correction plate 7F is installed in apredetermined position within the illumination optical path.

Additionally, it goes without saying that the above describedmanufacturing of the illumination NA correction plate 7F andillumination NA correction using this plate must be performed prior tothe various measurement operations using the test reticle TR when theimage distortion correction plate G3, the astigmatism/coma aberrationcorrection plate G3, and the image plane curvature correction plate G4are manufactured.

Meanwhile, as shown in FIG. 1, the spatial filter 7H is arranged to beswitchable on the exit side of the second fly-eye lens 7G in order tochange the shape or the size of the light source image SSi formed in thepupil Ep of the projection optical system PL. Therefore, if the apertureof the spatial filter 7H is switched from a normal circular aperture toan annular aperture, or from the annular aperture to 4-aperture, theoptical characteristic of illumination luminous flux which irradiatesthe reticle R or the test reticle TR may differ, so that also aninfluence on the projection optical system PL may differ.

Accordingly, it is desirable that each of the above described imagedistortion correction plate G1, astigmatism/coma aberration correctionplate G3, image plane curvature correction plate G4, illumination NAcorrection plate 7F is configured to be exchangeable for an optimumplate according to the shape of the aperture of the spatial filter 7H inaccordance with the switching of the spatial filter 7H.

FIG. 9 shows the outline of the configuration of a projection exposureapparatus where the image distortion correction plate G1, theastigmatism/coma aberration correction plate G3, the image planecurvature correction plate G4, and the illumination NA correction plate7F are respectively made exchangeable, and the fundamental arrangementof the respective optical components from the collective lens 7E withinthe illumination optical system to the projection image plane PF3 of theprojection optical system PL is the same as that in the configuration ofFIG. 1. In FIG. 9, the image distortion correction plate G1 is arrangedto be exchangeable for a plurality of image distortion correction platesG1′ which are polished beforehand according to the shape or the size ofthe aperture of the spatial filter 7H and are in stock in a library 220,and its exchange operations are performed by an automatic exchangemechanism 222 which operates in response to the command from the maincontrol system 32.

Additionally, on a switch mechanism 224 such as a turret, a linearslider, etc., a plurality of illumination NA correction plates 7F can bemounted, and each of the correction plates 7F is pre-manufactured sothat a dynamic illumination NA difference becomes a minimum according tothe shape or the size of the aperture of the spatial filter 7H. Whichillumination NA correction plate to select is determined incorrespondence with the spatial filter 7H selected in response to thecommand from the main control system 32.

Also for the astigmatism/coma correction plate G3 and the image planecurvature correction plate G4, a plurality of plates pre-manufactured incorrespondence with the switching of the spatial filter 7H are in stockin a library 226, and suitable correction plates G3 and G4 among themare selected by an automatic exchange mechanism 227 in response to thecommand from the main control system 32, and inserted in the bottom ofthe projection optical system PL.

Also for the telecentric correction plate 7N, an automatic exchangemechanism 228 for exchanging for a telecentric correction plate which ispolished beforehand according to an illumination condition (spatialfilter 7H) in response to the command from the main control system 32 isarranged. However, only if an average telecentric error in the whole ofillumination luminous flux is equally corrected, the automatic exchangemechanism 228 may be configured merely by an actuator which adjusts atilt of the telecentric correction plate 7N to be two-dimensional.

With the above described configuration, the respective fluctuations ofthe optical characteristic of illumination luminous flux and the imageformation characteristic of the projection optical system PL, whichoccur with an illumination condition change, can be optimally correctedin response to the command from the main control system 32, and an imageof the pattern formed on the reticle R can be projected and transferredonto the wafer W in a state where few aberrations (such as a distortionerror including an isotropic magnification error, an image planecurvature error, an astigmatism/coma error, a telecentric error, etc.)exist in all cases.

The projection optical system PL exemplified in the above describedembodiments is assumed to be a reduction projection lens configured onlyby a dioptric element (lens) which uses quartz or fluorite as an opticalglass material. However, the present invention can be applied also toother types of a projection optical system in exactly the same manner.Accordingly the other types of a projection optical system will bebriefly explained by referring to FIG. 10.

FIG. 10(A) is a reduction projection optical system where dioptricelements (lens systems) GS1 through GS4, a concave mirror MRs, and abeam splitter PBS are combined. The characteristic of this system is apoint that the image luminous flux from the reticle R is reflected bythe concave mirror MRs via the large beam splitter PBS, and againreturned to the beam splitter PBS, and imaged on the projection imageplane PF3 (wafer W) with a reduction ratio earned at the dioptric lenssystem GS4. Its details are disclosed by the Japanese laid-openPublication No. 3-282527 (NC).

FIG. 10(B) is a reduction projection optical system where dioptricelements (lens systems) GS1 through GS4, a small mirror MRa, and aconcave mirror MRs are combined. The characteristic of this system is apoint that the image luminous flux from the reticle R is imaged on theprojection image plane PF3 (wafer W) through a first image formationsystem PL1 which is almost an equimultiple and composed of lens systemsGS1 and GS2 and a concave mirror MRs, and a second image formationsystem PL2 which is composed of lens systems GS3 and GS4 and has almosta desired reduction ratio. Its details are disclosed by the Japaneselaid-open Publication No. 8-304705 (NC: Takahashi).

FIG. 10(C) is an equimultiple projection optical system where a dioptricelement (lens system) GS1 and a concave mirror MRs are combined. Thecharacteristic of this system is a point that the image luminous fluxfrom the reticle R is imaged on the projection image plane PF3 (wafer W)as an equimultiple orthoscopic image through first and second Dysonimage formation systems PL1 and PL2, which are respectively configuredby a prism reflection mirror MRe, the lens system GS1, and the concavemirror MRs. Its details are disclosed by the Japanese laid-openPublication No. 7-57986 (NC: Tanaka).

Also to the exposure apparatus comprising each of the projection opticalsystems shown in FIGS. 10(A), 10(B), and 10(C), the above describedimage distortion correction plate G1, astigmatism/coma correction plateG3, and image plane curvature correction plate G4 can be attached in asimilar manner. Since an intermediate image formation plane PF4 which isalmost an equimultiple of a pattern within an illumination area on thereticle R is formed especially in the projection optical system of FIGS.10(B) and 10(C), at least one of the image distortion correction plateG1, the astigmatism/coma correction plate G3, and the image planecurvature correction plate G4 can be arranged in the neighborhood of theintermediate image formation plane PF4.

Additionally, the projection optical systems shown in FIGS. 10(A),10(B), and 10(C) are systems which can be sufficiently applied to anultraviolet light having a central wavelength of 200 nm or less such asan ArF excimer laser beam, etc. by selecting an optical glass material,a surface-coated material, etc. Even when such a projection opticalsystem is used, a significant effect such that a distortion of a patternimage which is finally transferred onto a photosensitized substrate, anabsolute projection position error, or a local overlapping error can besuppressed to one-tenth (approximately several tens of nms) or less ofthe minimum line width of the pattern image to be transferred bycarrying out the sequence of: (1) the measurement of dynamic opticalcharacteristics (a distortion, an astigmatism/coma aberration, anillumination NA difference, etc.) under a set illumination condition;(2) the process of each correction plate type based on the result of theabove described measurement; and (3) the mounting and the adjustment(including re-measurement) of each manufactured correction plate type,can be obtained.

In the meantime, the projection optical systems shown in FIGS. 1 and10(A) among the above described projection optical systems shown inFIGS. 1 and 10 possess a circular projection field, while the projectionoptical systems shown in FIGS. 10(B) and 10(C) possess almost asemicircle projection field. An effective projection area EIA which isrestricted to a rectangular slit shape within a projection field isassumed to be used for scan-exposure whichever projection optical systemis used. However, a slit projection area in an arc shape may be setdepending on a case.

In such a case, the shape of the intensity distribution of theillumination light which illuminates the reticle R (TR) may be merelymodified to be an arc-shaped slit. However, considering that theillumination light is a pulse light, it is not advantageous to make thewidth of the scanning direction of the arc-shaped slit as thin asdisclosed by pp. 424-433 in Vol. 1088 of the above described SPIE, whichis cited earlier in the explanation of the conventional technique, andsome width is required.

Assume that a width Dap of an arc-shaped slit in the scanning directionon a wafer is 1 mm, the number Nm (integer) of pulse lights to beemitted while the wafer is moving by that width during the scanning is20 pulses, and the maximum frequency fp of the pulse oscillation of anillumination. light is 1000 Hz (conforming to the standard of a laserlight source). The moving speed Vws of the wafer while one area on thewafer is being scan-exposed becomes 50 mm/sec based on the relationshipVws=Dap/(Nm/fp), which proves that a throughput is improved with thewidening of the slit width Dap.

Accordingly, even if an illumination light is set to have an arc-shapedslit, a width of approximately 3 to 8 millimeters, which is wider than aconventional method, must be adopted on a wafer. However, it isdesirable not to make the inside arc of the illumination light havingthe arc-shaped slit and its outside arc concentric, but to form the slitinto a crescent shape such that the width of scan-exposure of thearc-shaped slit is the same at any position in the non-scanningdirection of the arc-shaped slit.

The way of thinking of the respective optical aberration corrections bythe image distortion correction plate G1, the astigmatism/comacorrection plate G3, the image plane curvature correction plate G4, thetelecentric correction plate 7N, and the illumination NA correctionplate 7F, which is explained in the embodiments of the presentinvention, is applicable also to an X-ray exposure apparatus whichcomprises a reduction projection system configured only by catoptricelements (a concave mirror, convex mirror, a toroidal reflection mirror,a plane mirror, etc.) in addition to the projection optical systemconfigured by a catadioptric system (a system where a dioptric elementand a catoptric element are combined) shown in FIG. 10.

Because there is no optical material having a satisfactory dioptricoperation for an ultra-high-frequency illumination light, corrections ofthe distortion characteristic, the astigmatism/coma aberrationcharacteristic, the telecentric characteristic, etc. can be implementedby locally and infinitesimally transforming the plane shape of thereflection surface of a catoptric element in a dedicated manner. As themethod for performing an infinitesimal transformation, for example, themethod for polishing a reflection layer, which is piled up relativelythick, on the surface of the material (low-expansion glass, quartz, fineceramics, etc.), which becomes a preform of a reflection mirror arrangedat a position close to the object or the image plane within a projectionoptical path, the method for intentionally performing an infinitesimaltransformation for the shape of a reflection plane in a controllablerange by applying a local stress to a preform from the rear or the sideof the reflection plane of a reflection mirror, the method forinfinitesimally transforming the shape of a reflection plane withthermal expansion by installing a temperature adjuster (Peltier element,heat pipe, etc.) on the rear of a reflection mirror, etc. areconsidered.

Meanwhile, when the image distortion correction plate G1 ismanufactured, when the telecentric correction plate 7N is manufactured,or when the astigmatism/coma aberration correction plate G3 ismanufactured, the dynamic distortion characteristic, the dynamictelecentric error characteristic, or the dynamic astigmatismcharacteristic, etc. in consideration of the averaging at the time ofscan-exposure must be obtained by measurements. However, such types ofdynamic aberration characteristics can be obtained also from the resultof the test printing of a measurement mark pattern on the test reticleTR with a scan-exposure method. Therefore, the measurement method andsequence in that case will be explained below by referring to FIGS. 11and 12.

As explained earlier, if a particular object point positioned on theobject plane of the projection optical system PL is transferred on thewafer W by using the exposure apparatus shown in FIG. 1, the image ofthe object point projected onto the wafer W is modulated by the staticdistortion characteristic at each position in the scanning directionwithin the effective projection area EIA of the projection opticalsystem PLM, and is averaged, so that the projection image formed on thewafer W has already included a dynamic distortion characteristic(dynamic image distortion error).

Accordingly, if a measurement mark on the test reticle TR isscan-exposed onto a test wafer, each L&S pattern projection image formedat the position of an ideal lattice point or its equivalent positionbecomes an image accompanying a dynamic image distortion vector(distortion error).

Therefore, as shown in FIG. 11, a resist layer is coated on a superflatwafer W having a notch NT, which is suitable for test printing, and thewafer is mounted on the table TP of the exposure apparatus shown in FIG.1. Then, pattern areas on the test reticle TR are sequentiallytransferred, for example, in 3×3 shot areas TS1 through TS9 on the waferW with a step-and-scan method. At this time, the respective shot areasTS1 through TS9 shown in FIG. 11 are scanned in an order of TS1, TS2, .. . , TS9 alternately in the Y direction as indicated by the arrows inthis figure.

As a result, each projection image TM′(i,j) of the test mark TM(i,j)arranged in a matrix state on the test reticle R is transferred in therespective shot areas TS1 to TS9 of the resist layer on the wafer W as alatent image, as expanded and shown in the lower portion of FIG. 11.Then, the wafer W is transmitted to a coater developer, and the resistlayer is developed under the condition equal to that at the time of themanufacturing of an actual device.

The developed wafer W is set up within a dedicated examinationmeasurement device, by which a position deviation amount of eachprojection image TM′(i,j) formed by the concave/convex of the resistlayer within the respective shot areas TS1 through TS9 from an ideallattice point is measured. The projection image TM′(i,j) measured atthat time may be any image of an L&S pattern, a cross-shaped LAMPASmark, a vernier mark, etc., an image suitable for the examinationmeasurement device is used.

For the position deviation measurement of each projection image TM′(i,j)from an ideal lattice point, an alignment detection system included in aprojection exposure apparatus may be used. The wafer W after beingdeveloped is mounted, for example, within the projection exposureapparatus equipped with an LSA system, an FIA system, or an LIA system,which is disclosed by the Japanese laid-open Publication No. 2-54103,and a pattern and a mark formed on the resist layer can be measured in asimilar manner.

The position deviation amount of each projection image TM′(i,j) from anideal lattice point, which is obtained by the above describedmeasurement operation, becomes an amount that directly represents thedynamic image distortion at each ideal lattice point.

However, respective image distortions of a plurality of projectionimages TM(i,j), which exist, for example, respectively along lines JLa,JLb, and JLc extending in the scanning direction (X direction), amongprojection images TM′(i,j) are calculatedly averaged for the respectivelines JLa, JLb, and JLc. This is because unevenness occurs due to themove control precision of a reticle stage or a wafer stage at the timeof scan-exposure, or a measurement error of a projection image TM′(i,j)if the dynamic image distortion characteristic is determined with onlyone particular combination.

In this way, the dynamic distortion characteristic at the position inthe line JLb within the effective projection area EIA or in itsneighborhood can be accurately obtained from the average value of therespective image distortions of the plurality of projection imagesTM′(i,j) in the line JLb. However, if the respective image distortionsof all the projection images TM′(i,j) which exist along the respectivelines JLa, JLb, and JLc are averaged within a shot area TSn, also themoving errors (a relative rotation error of a scanning axis, a yawingerror, etc.) of the reticle stage 8 and the wafer stage 14 at the timeof scan-exposure are averaged in the size of the scanning directionwithin the shot area TSn.

Therefore, as shown in FIG. 12, the dynamic image distortion is obtainedfor each of the rightmost combination GF(1), the middle combinationGF(2), and the leftmost combination GF(3) in the scanning direction (Ydirection) within the shot area TSn by an actual measurement, and theactually measured image distortion from which the moving errors of thestages 8 and 14 at each scanning position (position in the Y directionwithin the shot area) are subtracted is defined to be a dynamicdistortion characteristic.

Then, the distortion characteristics of the respective combinationsGF(1), GF(2), and GF(3) from which the moving errors are subtracted areaveraged. Notice that it is easy to calculatedly obtain the movingerrors of the stages 8 and 14 afterwards, if the measurement value(X,Y,θ) by the interferometers 46, 62, etc. at the time of scan-exposureis stored in real time in a neighborhood range of the scanning positionof each of the combinations GF(1), GF(2), and GF(3).

Additionally, if the dynamic image distortion at an arbitrary positionin the X direction is determined in each of the combinations GF(1),GF(2), and GF(3), averaging may be made by using the result of an actualmeasurement of the image distortion of a projection image TM′(i,j)positioned in the periphery of that position. For example, as shown inFIG. 12, if the image distortion on the line JLb in the combinationGF(1) is determined based on the assumption that the upper right cornerof the projection image TM′(i,j) is TM′(0,0), the actual measurementvalues of the image distortions of the projection image TM′(7,1) at thatposition and its peripheral projection images TM′(6,0), TM′(6,2),TM′(8,0), and TM′(8,2) are averaged.

Similarly, if the image distortion on the line JLd (the position next tothe line JLb) in the combination GF(1) is determined, the actualmeasurement values of the image distortions of the projection imagesTM′(5,1), TM′(6,0), TM′(6,2), and TM′(7,1), which are positioned in theperiphery of that position, are averaged. If the image distortion on theline JLb in the combination GF(2) is determined, the actual measurementvalues of the image distortions of 4 projection images TM′(i,j) existingin an ellipse Gu(i,j) with that position as a center are averaged.

Furthermore, in this embodiment, a plurality of shot areas TSn areformed on the wafer W. Therefore, if the image distortion on theparticular position in the shot area is determined, there is anadvantage that a random measurement error can be reduced by adding andaveraging the dynamic image distortion (for which a moving error iscorrected) at the same position in the other shot areas.

Here, FIG. 13 illustratively showing the entire appearance of theprojection exposure apparatus shown in FIG. 1 is explained. Theconstituent elements having the same capabilities as those shown in FIG.1 are denoted with the same reference numerals.

The projection exposure apparatus shown in FIG. 13 uses an ultravioletpulse laser beam from the excimer laser light source 1 in order toobtain the pattern resolution of the minimum line width of 0.3 to 0.15μm or so, which is required to mass-produce a micro circuit devicehaving the integration degree and minuteness equivalent to asemiconductor memory element (D-RAM) of 64M to 1G bits or more.

The wavelength width of the excimer laser beam is narrowed to includewithin a tolerable range the color aberration caused by various dioptricelements configuring the illumination system or the projection opticalsystem PL of the exposure apparatus. The absolute value of the centralwavelength to be narrowed or the value of the width to be narrowed isdisplayed on an operation panel 2, and can be infinitesimally adjustedfrom the operation panel 2 depending on need. Additionally, pulsed lightemission mode (representatively, three modes such as self-excitedoscillation, external trigger oscillation, and maintenance oscillation)can be set from the operation panel 2.

Because the excimer laser light source 1 is normally arranged in a room(service room with a lower cleanness degree), which is isolated from asuper-clean room where an exposure apparatus itself is installed, alsothe operation panel 2 is arranged within that service room. Furthermore,a control computer interfaced with the operation panel 2 is included inthe excimer laser light source 1. While normal exposure operations areperformed, this computer controls the pulsed light emission of theexcimer laser light source 1 in response to the instruction from aminicomputer 32 for controlling the exposure apparatus, which will bedescribed later.

The excimer laser beam from the excimer laser light source 1 is led to abeam reception system 5 of the exposure apparatus via a shading tube 3.Within the beam reception system 5, a plurality of movable reflectionmirrors for optimally adjusting the incidence position and angle of theexcimer laser beam to the illumination optical system 7 of the exposureapparatus, so that the excimer laser beam always enters into theillumination optical system 7 in a predetermined positional relationshipto the optical axis of the illumination optical system 7.

Within the illumination optical system 7, as explained in detail byreferring to FIG. 1, a variable beam attenuator for adjusting averageenergy for each pulse of the excimer laser beam, a fly-eye lens (opticalintegrator) system for making the excimer laser beam into anillumination light having an even intensity distribution, a reticleblind (illumination field diaphragm) for restricting a reticleillumination light at the time of scan-exposure to a rectangular-slitshape, an image formation system (including condenser lens) for imagingthe rectangular-slit-shaped aperture of the blind in a circuit patternarea on a reticle, etc. are arranged.

The rectangular-slit-shaped illumination light irradiated on the reticleis set to extend long and narrow in the X direction (non-scanningdirection) in the center of the circular projection field of theprojection optical system PL in FIG. 13. The width of the illuminationlight in the Y direction (scanning direction) is set to be almostconstant.

The reticle is absorbed and held on a reticle stage 8, which linearlymoves on a reticle base 10 with a large stroke by a linear motor, etc.,for being scan-exposed, and is set to be infinitesimally movable by avoice coil motor (VCM), a piezo element, etc. also in the X and the θdirections. The reticle base 10 is securely disposed on the top of fourcolumns 11 standing upward from a main body column base 12 which fixesthe flange of the projection optical system PL.

The main body column base 12 is formed in a box shape, the inside ofwhich is made hollow in this embodiment, and a base 15 for supporting amovable stage 14 on which a wafer W is mounted is fixed in its follow.FIG. 13 shows only a laser interferometer 16X for measuring the positionof the movable stage 14 in the X direction. Actually, however, a laserinterferometer 16Y for measuring the position of the movable stage 14 inthe Y direction is arranged in a similar manner. The movable stage 14 inFIG. 13 is assumed to stop at the loading position for receiving thewafer W held by the tip of an arm 22 of a wafer conveying robot 20, orthe unloading position for handing the wafer on the holder of themovable stage 14 to the arm 22.

Furthermore, a mounting stand 18 with a shockproof capability, which isintended to support the entire apparatus from floor, is arranged at eachof the four corners of the main body column base 12. The mounting stand18 supports the weight of the whole of the apparatus itself via an aircylinder, and comprises an acutuator and various sensors for activelycorrecting the tilt of the entire apparatus, the displacement in the Zdirection, and the displacements of the entire apparatus in the X andthe Y directions by using feedback or feedforward control.

The entire operations of the main body of the exposure apparatus shownin FIG. 13 are managed by a control rack 30 which includes a pluralityof unit control boards 31 for individually controlling the constituentelements (excimer laser light source 1, illumination optical system 7,reticle stage 8, wafer movable stage 14, conveying robot 20, etc.)within the main body of the apparatus, the minicomputer 32 forintegratedly controlling the control boards 31, an operation panel 33, adisplay 34, etc. A unit computer such as a microprocessor etc. isarranged within each of the control boards 31. These unit computerscooperate with the minicomputer 32, so that the sequence of an exposureprocess is performed for a plurality of wafers.

The entire sequence of the exposure process is managed by the processprogram stored in the minicomputer 32. With the process program, theinformation about a wafer to be exposed (the number of wafers to beprocessed, shot size, shot array data, alignment mark arrangement data,alignment condition, etc.), the information about a reticle to be used(the type data of a pattern, the arrangement data of each mark, the sizeof a circuit pattern area, etc.), and the information about exposureconditions (the amount of exposure, the amount of focus offset, theoffset amount of scanning speed, the offset amount of projectionmagnification, the correction amount of various aberration or imagedistortion, settings of a ò value or an illumination NA, etc. of anillumination system, settings of the NA value of the projection lenssystem, etc.) are stored as a parameter group package under the exposureprocess file name created by an operator.

The minicomputer 32 decodes the process program instructed to beexecuted, and instructs corresponding unit computers of the operationsof the respective constituent elements, which are required for exposingwafers one after another as commands. When each of the unit computerssuccessfully terminates one command, it transmits the status indicatingthe successful termination to the minicomputer 32. The minicomputer 32which receives this status issues the next command to a unit computer.When a wafer exchange command is issued from the minicomputer 32 duringsuch a process sequence, the control units of the movable stage 14 andthe wafer conveying robot 20 collaborate with each other, so that themovable stage 14 and the arm 22 (wafer W) are set to have the positionalrelationship shown in FIG. 13.

Furthermore, a plurality of pieces of utility software relating to thepracticing of the present invention are installed in the minicomputer32. Typical of the software are two types: (1) the measurement programfor automatically measuring the optical characteristic of a projectionoptical system or an illumination optical system, and for evaluating thequality (distortion characteristic, astigmatism/coma characteristic,telecentric characteristic, illumination numerical aperturecharacteristic, etc.) of a projection image; and (2) the correctionprogram for performing respective correction processes according to theevaluated quality of the projection image). These programs areconfigured to operate in cooperation with the corresponding constituentelements in FIG. 1 which shows the details of the configuration of theapparatus shown in FIG. 13.

Note that the laser interferometer 16X in FIG. 13 corresponds to thelaser interferometer 62 in FIG. 1.

Next, the operation, the configuration, and the manufacturing method ofthe above described image distortion correction plate G1 will bedescribed in detail. The manufacturing method is based on the onerecited in the above cited Japanese Unexamined Patent Publication No.8-203805 (Nikon). However, there is a difference in a point that thismanufacturing method is applied to the projection optical system forscan-exposure.

First of all, the distortion characteristic of the projection opticalsystem having a circular projection field is briefly explained byreferring to FIG. 14.

In FIG. 14, a circular projection field IF represents the field of thewafer W side (image plane side), and the origin of a coordinate systemX-Y is assumed to agree with the optical axis AX of the projectionoptical system PL. Additionally, a plurality of points GP(Xi,Yj), whichare regularly arranged in the coordinate system X-Y in FIG. 14 representthe ideal lattice points with the optical axis AX as the origin. Anarrow at each of the ideal lattice points GP(Xi,Yj) represents theamount of distortion (image distortion vector) DV(Xi,Yj) at its positionon the image plane.

As is known from the distortion characteristic shown in FIG. 14, theprojection optical system of this type can suppress the image distortionvector to 20 nm or less in the neighborhood of the optical axis AX.However, also the absolute value of the image distortion vector normallyincreases as it approaches the circumference of the projection field IF.If image distortion vectors DV(Xi,Yj) conform to a simple functionaccording to the image height value (the distance from the optical axisAX) or the X-Y position, it becomes possible to reduce all of the imagedistortion vectors DV(Xi,Yj) within the projection field IF by using themovable lens element G2 or the lens control system 44 to which thecorrection according to the function can be made.

However, as is understood from the distortion characteristic shown inFIG. 14, the respective image distortion vectors DV(Xi,Yj) includesmutually random components. Even if a correction according to aparticular function is made, the random components still remain. Suchremaining random error components included in the image distortionvectors DV(Xi,Yj) emerge as random distortion errors unchanged atrespective points in a projected circuit pattern image, when beingstatically exposed.

In the meantime, when being scan-exposed, the image distortion vectorwhich statically occurs at each of a plurality of image points existingin the move direction of the wafer W emerges as a dynamic imagedistortion vector averaged or accumulated within an effective exposurefield (the width of an exposure slit). In this case, even if the staticdistortion characteristic conforming to a particular function iscorrected, the random image distortion vector consequently remains dueto the random distortion error component remaining at each point on animage plane.

Arranged to reduce such a random image distortion vector and to obtainthe best distortion characteristic at the time of scan-exposure is theimage distortion correction plate G1 shown in FIG. 1. The correctionplate G1 in this embodiment is configured in such a way that part of thesurface of a quartz or fluorite parallel plate is polished with anaccuracy of a wavelength order, and a predetermined infinitesimal slopeis formed in part of the surface. By deflecting the principal ray oflocal image luminous flux, which passes through the infinitesimal slope,by an extremely slight amount, the static image distortion vector on theimage plane is changed.

Here, the relationship between the static distortion characteristicoccurring within the projection filed IF and the dynamic distortioncharacteristic occurring at the time of scan-exposure is explained byreferring to FIG. 15. FIG. 15 assumes that the circular field IFrepresents the field on the image plane side of the projection opticalsystem PL, and the origin of the coordinate system X-Y exists in itscenter (the position of the optical axis AX).

Since the reticle R and the wafer W are scanned relatively in the Ydirection in the apparatuses shown in FIGS. 1 and 13, the effectiveprojection area EIA has an even width which is symmetrical with respectto the X axis in the Y direction, and is set to be a long and thinrectangle or slit shape. The area EIA is actually determined accordingto the distribution of the illumination light to the reticle R, which isstipulated by the aperture of the blind 7L shown in FIG. 1. However,this area may be similarly stipulated by arranging a field diaphragmwith a rectangular aperture on the intermediate image formation plane inthe projection optical system PL, depending on the configuration of theprojection optical system PL.

In FIG. 15, ideal lattice points GP(Xi,Yj), which are arranged as 13lines (SL1 to SL13) in the X direction and as 7 lines (1 to 7) in the Ydirection are set within the area EIA. The subscript “i” of the ideallattice point GP(Xi,Yj) indicates any of integers 1 through 13, whilethe subscript “j” indicates any of integers 1 through 7. The latticepoint GP(X7,Y4) of i=7 and j=4 is positioned in the center of thecircular field IF.

The image distortion vector occurring at each of the ideal latticepoints GP(Xi,Yj) is a static distortion characteristic. Here, staticimage distortion vectors DV(1,p1) to DV(1,p7) at seven lattice pointsGP(X1,Y1) to GP(X1,Y7) in the line SL1, which exist in sequence in the Ydirection being the scan-exposure direction, are shown as an example.The image distortion vectors DV(1,p1) to DV(1,p7) are represented as thesegments extending from the white circles which represent the positionsof the ideal lattice points in the line SL1.

In the static exposure, the pattern at one point on the reticle R isprojected only with the image distortion vector at that point. In themeantime, in the scan-exposure, the image of the pattern at one point onthe reticle R is projected while moving the pattern, for example, alongthe line SL1 in the Y direction within the projection area EIA at anequal speed. Therefore, the pattern image at that point is affected byall of the static image distortion vectors DV(1,p1) to DV(1,p7) shown inFIG. 15, and formed on the wafer W.

When the projection image of the pattern at the one point on the reticleR is moved linearly within the projection area EIA in the Y direction,the position of the reticle R is controlled in the X, Y, and edirections by the laser interferometer 46 with an overall accuracy of±15 nm or less, as shown in FIG. 1. Accordingly, the linearity of themovement of the projection image is reduced by the amount equivalent tothe projection magnification, and can be sufficiently made smaller thanthe image distortion vectors DV(1,p1) to DV(1,p7). Therefore, theprojection image of the pattern at one point on the reticle R, which isformed on the wafer W by scan-exposure, becomes the one accompanying thedynamic image distortion vector VP(SL1) obtained by averaging the imagedistortion vectors DV(1,p1) to DV(1,p7) that the projection opticalsystem PL possess, in almost any case.

Accordingly, the dynamic image distortion vector VP(SL1) obtained in theline SL1 in the scanning direction within the projection area EIA isacquired by calculating the average value of the X direction componentsof the static image distortion vectors DV(1,p1) to DV(1,p7) and theaverage value of their Y direction components. Such a dynamic imagedistortion vector VP(Xi) is obtained for each of the lines SL1 to SL13in the X direction, so that the distortion characteristic of the patternimage (or the ideal lattice point image) to be transferred onto thewafer W as a result of the scan-exposure through the projection area EIAcan be determined.

In the scan-exposure system, if the scan-moving for the reticle R andthe wafer W is precisely performed, the distortion characteristicoccurring in the whole of one shot area on the wafer W conforms to thedynamic image distortion vector VP(Xi) at any point within that shot.Therefore, the distortion characteristic caused by the scan-exposure isidentified as the dynamic image distortion vector VP(Xi) occurring ateach of the ideal lattice points which are arranged in sequence in the Xdirection, for example, as shown in FIGS. 16A to 16D.

FIGS. 16A to 16D exemplify the dynamic image distortion vector VP(Xi)(i=1 to 13) which has a tendency varying according to the staticdistortion characteristic in the projection area EIA within the circularfield IF. FIG. 16A exemplifies the distortion characteristic which has atendency such that each dynamic image distortion vector VP(Xi) becomesalmost parallel to the scanning (Y) direction, and its absolute value isapproximate to a linear function which varies almost at a constant ratioaccording to the position in the X direction.

FIG. 16B exemplifies the distortion characteristic which has a tendencysuch that each dynamic image distortion vector VP(Xi) becomes almostparallel to the scanning (Y) direction, and its absolute value is almostapproximate to a quadratic function according to the position in the Xdirection. FIG. 16C exemplifies the distortion characteristic which hasa tendency such that the tendency of the distortion characteristic shownin FIG. 16B is superposed with the magnification error in thenon-scanning direction. FIG. 16D exemplifies the distortioncharacteristic which has a tendency such that each dynamic imagedistortion vector P(Xi) varies due to random directionality andmagnitude.

Assume that the image distortion vectors VP(Xi) are measured for each ofcombinations GF(1) and GF(2) of the projection image TM′(i,j) existingin sequence in the non-scanning (X) direction in one shot area TS9 inFIG. 11. The image distortion vectors in each of the combinations GF(1)and GF(2) directly represent, for example, the distortioncharacteristics shown in FIG. 16D.

The dynamic distortion characteristic shown in FIG. 16A is, what iscalled, a skew. Except for correcting the characteristic of theprojection optical system PL itself with the surface configuration ofthe correction plate G1, the above described distortion characteristiccan be corrected by performing scanning exposure in the state where thereticle R and the wafer W are infinitesimally rotated relatively fromthe initial state. Additionally, for the dynamic distortioncharacteristic shown in FIG. 16B, a correction can be also made byinfinitesimally tilting the lens system G2, the astigmatism/comacorrection plate G3, the image distortion correction plate G1, thereticle R, or the wafer W relatively to the plane vertical to theoptical axis AX of the projection lens system PL, except for correctingthe characteristic of the projection optical system PL itself with thesurface configuration of the correction plate G1.

Furthermore, for the dynamic distortion characteristic shown in FIG.16C, a correction can be made both by infinitesimally tilting the lenssystem G2, the astigmatism/coma correction plate G3, the imagedistortion correction plate G1, the reticle R, or the wafer W similar toFIG. 16B, and by adjusting the magnification with the infinitesimalparallel translation toward the direction of the optical axis AX of thelens system G or with the pressure control of the air chamber within theprojection optical system PL, except for correcting the characteristicof the projection optical system PL itself with the plane shape of thecorrection plate G1.

Still further, if each dynamic image distortion vector VP(Xi) tends tobe random as shown in FIG. 16D, a means is taken to correct thecharacteristic of the projection optical system PL itself with thesurface configuration of the correction plate G1. The random distortioncharacteristics shown in FIG. 16D are also superposed on and emerge asthe distortion characteristics which can be function-approximated asshown in FIGS. 16A through 16C. Therefore, even if the distortioncomponents which can be function-approximated are corrected, the randomdistortion components still remain. Accordingly, it is desirable thatthe distortion correction with the surface configuration process of thecorrection plate G1 is made mainly for the random component of thedynamic distortion characteristic.

Hence, the method for manufacturing the image distortion correctionplate G1 preferable for correcting the dynamic random distortioncharacteristics shown in FIG. 16D is explained by referring to FIGS.17A, 17B, 18 and 19. FIG. 17A exemplifies the random distortioncharacteristics VP(X1) to VP(X13) measured in the state where an imagedistortion correction plate G1 yet to be processed is arranged in apredetermined position in the image formation optical path by theprojection optical system PL. FIG. 17B exemplifies the dynamicdistortion characteristics VP′(X1) to VP′(X13) after the characteristicsshown in FIG. 17A are corrected with the image distortion correctionplate G1.

As the correction for random distortion characteristics, there are twoways of thinking: the method (zero correction) for reducing to “0” asclose as possible each of the dynamic image distortion vectors VP(X1) toVP(X13) at the respective accumulation image points existing in sequencein the non-scanning (X) direction as shown in FIG. 17A; and the method(function correction) for approximating each of the image distortionvectors VP(X1) and VP(X13) to a certain tendency of a linear, aquadratic function, etc.

Here, the function correction method shown in FIG. 17B is assumed to beadopted to obtain the advantage that the polishing process of the imagedistortion correction plate G1 is relatively facilitated. However, ifthe image distortion vectors VP(X1) to VP(X13) are not so large, thezero correction may be applied to reduce the random dynamic distortioncharacteristics to “0”. Whichever method is adopted, the posture(especially, the tilt) of a processed image distortion correction plateG1 must be adjusted by an infinitesimal amount when being re-inserted inthe projection optical path.

The distortion characteristics VP′(X1) to VP′(X13) shown in FIG. 17Bare, here, corrected to have a predetermined offset amount in thescanning (Y) direction, and to have a constant magnification error inthe non-scanning (X) direction at the same time. Both of the offsetamount and the magnification error can be approximate to a linearfunction, and can be sufficiently corrected with another correctionmechanism such as the image shift adjustment by an infinitesimal tiltaround the X axis of the image distortion correction plate G1, themagnification adjustment by the lens element G2 within the projectionoptical system PL, etc.

To process the image distortion correction plate G1, the imagedistortion vectors VP(X1) to VP(X13) causing the dynamic distortioncharacteristics shown in FIG. 17A must be first measured. There are twotypes of the measurement method: the offline measurement by testprinting (test exposure); and the onbody measurement with the imagedetector KES securely disposed on the wafer table TB of the projectionexposure apparatus shown in FIG. 1.

With the test exposure method, the test marks formed at an ideal latticepoint on a test reticle are statically transferred onto the wafer W theflatness of which is strictly managed, the exposed wafer W is conveyedto a measurement device different from the projection exposure apparatusafter being developed, and the coordinate positions and the positionsdeviation amount of the transferred test marks are measured, so that thestatic image distortion vectors at respective points within the circularfield IF or the effective projection area EIA of the projection opticalsystem PL are obtained.

In the meantime, with the method using the space image detector KES, thewafer stage 14 is moved in the X and the Y directions to scan the imageof test marks formed at each ideal lattice point on a test reticle withthe knife-edge of the image detector KES while projecting the imageswith an illumination light for exposure, and the waveform of thephotoelectric signal output from the image detector KES at that time isanalyzed, so that static image distortion vectors are obtained.

As described above, with the onbody measurement method using the imagedetector KES, the data of the static image distortion vector at eachideal lattice point within the circular field IF or the effectiveprojection area EIA are sequentially stored in the storage medium of themain control system 32 shown in FIG. 1. Therefore, this method isconvenient to the case where the process of the image distortioncorrection plate G1 is simulated on software by using the stored data orto the case where the image distortion correction plate G1 is actuallypolished by a processor. Note that the details of the test exposure orthe distortion characteristic measurement with the image detector KESwill be described later.

When static image distortion vectors are obtained, the dynamicdistortion characteristics shown in FIG. 17A are obtained by averagingthe image distortion vectors in the Y direction within the rectangulareffective projection area EIA by a computer, a workstation, etc. Then, amodification vector (direction and magnitude) ΔVP(Xn) for each of theimage distortion vectors VP(X1) to VP(X13) shown in FIG. 17A isdetermined, for example, to obtain the dynamic distortioncharacteristics shown in FIG. 17B. That is, VP′(Xn)=VP(Xn)−ΔVP(Xn) (“n”is any of integers 1 to 13) determines the modification vector ΔVP(Xn).

Next, how to correct the static image distortion vector DV(i,pj) isdetermined for each point in the non-scanning (X) direction based on themodification vector ΔVP(Xn). Various methods may be considered for thisdetermination. Here, a correction is first made to the largest of thestatic image distortion vectors DV(i,p1) to DV(i,7) at seven points,which are shown in FIG. 15 and averaged in the Y direction, and thecorrection is made also to the image distortion vectors DV(i,pj) at theother points if the correction amount at the one point exceeds apredetermined tolerable value.

FIG. 18 exemplifies the image distortion vectors DV(i,p1) to DV(i,p7) atthe seven points, which exist in sequence in the Y (scanning) directionwithin the rectangular effective projection area EIA, and the dynamicimage distortion vector VP(Xn) obtained by averaging these vectors,wherein “n” and “i” are integer 1. In this figure, the target imagedistortion vector is VP′(Xn), while the modification vector is ΔVP(Xn).For the distortion characteristics shown in FIG. 18, the correctionbased on the modification vector ΔVP(Xn) is made mainly to the staticimage distortion vector DV(i,p1) at the point (i,p1). However, thecorrection is made also to the static image distortion vector DV(i,p2)at the point (i,p2) as the case may be.

Specifically, the correction is made so that the absolute value of theimage distortion vector DV(i,p7) or DV(i,p6) is reduced, and at the sametime, its directionality is infinitesimally changed. To implement this,the condition of the surface of the image distortion correction plate G1which infinitesimally deflects the principal ray passing through themeasurement point (ideal lattice point) within the projection field, atwhich the image distortion vector DV(i,p1) or DV(i,p2) is observed, maybe determined. This determining way is briefly explained by referring toFIGS. 19 and 20.

FIG. 19 is an enlarged view partially showing the positionalrelationship between the reticle R, the image distortion correctionplate G1, and the projection optical system PL (movable lens elementG2). Here, the first line in the Y direction among the plurality oflattice points GP(Xi,Yj) arranged in the rectangular projection area EIAin FIG. 15 is cross-sectioned in the X direction. Accordingly, thedirection of scan-exposure in FIG. 19 is the direction vertical to thesheet of this figure.

In FIG. 19, a test mark (vernier pattern for measurement, etc.) isformed at each position of an ideal lattice point on the pattern surfaceof the reticle R. Here, assume that a correction is made by locallypolishing a corresponding surface portion 9-9′ of the image distortioncorrection plate G1 for the image luminous flux LB(1,1) which originatesfrom the test mark at the lattice point GP(1,1) in the line SL1, wherethe image distortion vector DV(i,p1) shown in FIG. 18 occurs, and entersthe projection optical system PL, and for its principal ray ML(1,1).

To be more specific, the principal ray ML(1,1) is converted into aprincipal ray ML′(1,1) which is tilted by an infinitesimal amount in apredetermined direction by the local slope of the surface portion 9-9′in order to reduce the image distortion vector DV(i,p1) in FIG. 18. Atthis time, also the image luminous flux LB(1,1) from the lattice pointGP(1,1) is converted into image luminous flux LB′(1,1) which is tiltedby the infinitesimal amount by the local slope of the wavelength orderof the surface portion 9-9′. Also the principal rays passing through thelattice points GP(2,1) to G(7,1) among the other ideal lattice pointsGP(2,1) to GP(13,1) on the reticle R are indicated by broken lines.However, the correction is not made to these principal rays and imageluminous flux here.

FIG. 20 is an enlarged view of the local surface portion 9-9′ of theimage distortion correction plate G1 shown in FIG. 19, andexaggeratingly illustrates the tilt amount of the local slope formed inthe surface portion 9-9′ for ease of explanation. As explained in FIG.19, on the image distortion correction plate G1, the taper is formed inthe portion S(1,1), through which the principal ray ML(1,1) and theimage luminous flux LB(1,1) from the ideal lattice point GP(1,1) on thereticle R pass, by the tilt amount Δθ(1,1) according to the tilts of theprincipal ray ML′(1,1) and the image luminous flux LB′(1,1) to becorrected.

As explained earlier by referring to FIG. 18, the static imagedistortion vector DV(1,p1) occurring at the lattice point GP(1,1) mustbe corrected to be reduced in a negative direction in each of the X andthe Y directions. Actually, therefore, also the surface of the portionS(1,1) shown in FIG. 20 is infinitesimally tilted both in the X and theY directions. Additionally, the square of the polishing portion S(1,1)or its size in the X and the Y directions on the image distortioncorrection plate G1 is determined, ideally, in consideration of a spreadangle 2θna of the image luminous flux LB(1,1), which contributes to theprojection exposure, so that the image luminous flux LB(1,1) is almostentirely covered.

In an actual projection optical system PL, the numerical aperture (NAw)on the wafer W side is expected to be 0.6 to 0.8 or so. If theprojection magnification is reduced to one-fourth, the numericalaperture NAr on the reticle R side decreases to 0.15 to 0.2 or so. Sincethe numerical aperture NAr on the reticle side and the spread angle 2θnain FIG. 20 have a relationship of NAr=sin(θna), the square of theportion S(1,1) to be polished or the size in the X and the Y directionsis nonambiguously obtained from the relationship between an interval Hrbetween the pattern plane (back plane) of the reticle R and the surfaceplane of the image distortion correction plate G1, and the numericalaperture Nar.

Here, it is assumed that the correction is not made to the imagedistortion vector DV(1,p6) due to the image luminous flux including theprincipal ray ML(2,1) from the lattice point GP(2,1) positioned next tothe ideal lattice point GP(1,1) in the X direction. Therefore, theportion S(2,1) corresponding to the image luminous flux from the latticepoint GP(2,1) on the image distortion correction plate G1 is polished toremain parallel, as a matter of course.

Additionally, the portion S(0,1) at the left of the polished portionS(1,1) is polished to be a slope which rises to the left to revert tothe original parallel plane. However, this portion may be loosely joinedwith the surface of the portion S(1,1) in some cases depending onwhether or not the image luminous flux passing through the portionS(0,1) exists or whether or not the principal ray is corrected, asrepresented by an imaginary line. Furthermore, the parallel plane, whichis the surface of the non-polished portion, of the image distortioncorrection plate G1 is arranged vertically to the optical axis AX of theprojection optical system PL in FIGS. 19 and 20. However, if the entireimage distortion correction plate G1 itself is infinitesimally inclinedby the adjustment mechanism, the distortion characteristic (static imagedistortion vector) emerging on the projection image plane side can beinfinitesimally shifted in the X or the Y direction.

With the above described methods shown in FIGS. 19 and 20, the surfaceof the image distortion correction plate G1 is polished to be locallytilted along each of the 13 lines SL1 to SL13 existing in sequence inthe non-scanning direction so that the random distortion characteristicshown in FIG. 17A changes to the regular distortion characteristic shownin FIG. 17B.

FIG. 21 is a plan view of the image distortion correction plate G1manufactured by performing such a polishing process. In this embodiment,the entire shape of the image distortion correction plate G1 is set tobe a square similar to the reticle R. This is because the blanks(preform) of the reticle R, which is manufactured by strictly managingthe precision, the flatness degree, etc., can be used unchanged for theimage distortion correction plate G1. Needless to say, dedicated blanksboth sides of which are particularly polished may be used.

In FIG. 21, the rectangular effective projection area EIA and itsinternal 13×7 points are the same as those shown in FIG. 15. This figureassumes that the ideal lattice points positioned at the four cornersamong the 13×7 points are GP(1,1), (1,7), (13,1), and (13,7), and theideal lattice points positioned at both ends of the Y axis are GP(7,1)and (7,7). The area EIA′ spreading almost with a constant width outsidethe effective projection area EIA represents the spread portion of theimage luminous flux reaching the image distortion correction plate G1,which accompanies the numerical aperture NAr from the point positionedat the circumference of the projection area EIA on the reticle R.

In FIG. 21, each of shaded areas which are represented by circles orellipses for the sake of convenience S(1,a), S(2,a), S(3,a), S(4,a),S(5,a), S(6,a), S(7,a), S(8,a), S(9,a), S(10,a), S(11,a), S(12,a), andS(13,a) is a portion where a static image distortion vector is correctedby the polishing process shown in FIG. 20. The area S(1,a) among theareas S(i,a) and S(i,b) is equivalent to the above described polishingarea S(1,1) shown in FIG. 20.

As shown in FIG. 21, the polishing process for correcting the staticimage distortion vector VD(i,j) is basically performed for any one pointon the segments (scanning lines SL1 to S13 shown in FIG. 15) which linkthe seven lattice points existing in sequence in the scanning (Y)direction. However, a polishing area (taper portion) may be set in aplurality of portions in one scanning line like the areas S(6,a) andS(6,b) in FIG. 21, if the correction amount (the tilt amount bypolishing) at one point becomes too large, or depending on thedirectionality of the image distortion vector to be modified.

Additionally, the square of each of the polishing areas S(i,a) andS(i,b) or the taper amount and its tilt direction are determined withthe method explained in FIGS. 19 and 20. The plane which joins adjacentpolishing ares is polished to be smooth between the polishing areas.Furthermore, in FIG. 21, the polishing areas S(i,a) and S(i,b) arecomparatively set apart. Such an apart setting is advantageous to thepolishing process.

The reason is as follows: assuming that the tilt directions of thepolishing areas S(2,a) and (S3,a) which are adjacent each other in FIG.21 are calculated to be almost the same, a relatively acute reversetaper occurs at the boundary between the two polishing areas S(2,a) andS(3,a). Such a reverse taper gives the correction component thedirection of which is reverse to the originally intended imagedistortion vector correction, which also leads to the deterioration ofthe image quality of a projected reticle pattern.

Accordingly, if polishing areas which are adjacent in the Y direction onthe image distortion correction plate G1 have the same tilt direction onthe image distortion correction plate G1, it is good to again review thestatic image distortion vector DV(i,j) selected to put the abovedescribed dynamic distortion characteristic shown in FIG. 17A into thedesired state shown in FIG. 17B, and to shift both of the polishingareas in the X direction.

As described above, unlike the distortion characteristic correctionassuming static exposure, the static distortion characteristiccorrection assuming scan-exposure allows the polishing areas S(i,a) andS(i,b) on the image distortion correction plate G1 to scatter, whichleads to the advantage that the precision of the polishing process(especially, plane joining) can be relatively made moderate. Thisinversely means that the plane shapes of the specified polishing areasS(i,a) and S(i,b) can be precisely processed regardless of the planeshapes of the peripheral polishing areas.

In the meantime, the blanks for the image distortion correction plate G1shown in FIG. 21 is set on the X-Y stage of a dedicated polishingprocessor, precisely moved in the X and the Y directions relatively to arotary polishing head, and polished by pressing the rotary polishinghead into a desired polishing area at a calculated tilt angle with apredetermined force. In this case, the image distortion correction plateG1 after being processed must be accurately aligned with the positionsof the respective ideal lattice points within the projection field.Therefore, reference edges Pr-a, Pr-b, and Pr-c respectively contactingreference pins (rollers) KPa, KPb, and KPc arranged on the X-Y stage ofthe polishing processor or the support frame of the correction plate G1within the projection exposure apparatus, on one side of thecircumference of the image distortion correction plate G1, which isparallel to the Y axis, and on one side parallel to the X axis.

Here, one specific example of the polishing processor is explained byreferring to FIG. 22, although this is also disclosed by the JapaneseUnexamined Patent Publication No. 8-203805. In FIG. 22, the blanks ofthe image distortion correction plate G1 is mounted on a X-Y stage 101which can move on the main body of the polishing processor in the X andthe Y directions and is aligned by the reference pins KPa, KPb, and KPc.The X-Y stage 101 is moved by a driving mechanism 102, which is drivenby the instruction from a polishing control system 103.

The polishing control system 103 also controls the rotation of therotary polishing head 104 attached to the tip of a polishing unit 105,and an angle adjusting unit 106 which adjusts the angle at which the tipof the head 104 and the blanks (G1) contact. The polishing controlsystem 103 receives respective items of information such as the moveposition of the X-Y stage 101 and its moving speed during polishing, andthe rotation speed and the pressing force of the rotary polishing head104, the contact angle of the head 104, etc., which are analyzed by ananalyzing computer 107 based on the distortion characteristicmeasurement data from a data storage medium (disk, tape, card, etc.) oran online communication.

The above described polishing processor is arranged in the site where aprojection exposure apparatus is assembled and manufactured, and is usedat the step where the final image formation performance of the apparatusis examined and adjusted. As a matter of course, the polishing processorshown in FIG. 22 may be used on the assembly and manufacturing line ofthe projection optical system PL. In such a case, the image formationcharacteristic of the projection optical system PL which is simplexbefore being installed within the main body of the exposure apparatuscan be corrected with the correction plate G1. However, the imageformation characteristic in the simplex state of the projection opticalsystem PL may be slightly different from that in the state where theprojection optical system PL is installed within the main body of theapparatus. Accordingly, it is desirable to process the image distortioncorrection plate G1 with the polishing processor shown in FIG. 22 basedon the result (distortion characteristic) of examining the imageformation characteristic by using the illumination system of theexposure apparatus itself after the projection optical system PL isinstalled within the exposure apparatus.

Notice that the polishing processor shown in FIG. 22 may be used forperforming an aspheric process intended to correct the above describedtelecentric error for a particular lens element included in thecondenser lens systems 7K and 7Q shown in FIG. 1.

Meanwhile, the analyzing computer 107 of the polishing processor makes,for example, the determination of the respective polishing areas on theblanks of the image distortion correction plate G1 shown in FIG. 21, thedetermination of the surface configuration (mainly, the angle and thedirection of the inclination) in the respective polishing areas, etc.based on measured static or dynamic distortion characteristics.

At that time, the program which simulates the final state of thepolishing process based on the various measured distortioncharacteristic data and which is stored in the storing unit of theanalyzing computer 107 is performed, and the result of the simulation ismade visible on a display for an operator. In this way, the operator canverify the simulated state and condition of the polishing process on thedisplay, and he or she can set an optimum process state by preciselychanging and editing various parameters.

Thus manufactured image distortion correction plate G1 is securelydisposed on a support frame 120 shown in FIG. 23. On the support frame120, a rectangular aperture 120 a which does not shade the imageformation luminous flux passing through the effective projection areaEIA is formed, and a plurality of convex units 121 a to 121 k thatsupport the bottom of the image distortion correction plate G1 areformed in the periphery of the aperture 120 a.

The convex units 121 a to 121 d support almost four corners of the imagedistortion correction plate G1. The convex units 121 e to 121 h supportthe correction plate G1 in the neighborhood of the center of theaperture 120 a. The convex units 121 i and 121 j respectively supportthe centers of the right edge and the top edge of the correction plateG1. The convex unit 121 k supports the center of the bottom edge of thecorrection plate G1. With these convex units 121 a to 121 k, the imagedistortion correction plate G1 is mounted on the support frame 120 sothat its flexure is minimized.

Additionally, on the support frame 120, two reference rollers KPa andKPb contacting the reference side at the bottom of the image distortioncorrection plate G1, and one reference roller KPc contacting thereference side of the left of the image distortion correction plate G1are arranged to be rotatable. The image distortion correction plate G1is pressed toward the directions of the reference rollers KPa, KPb, andKPc by pressing elements 122 a and 122 b that are arranged to beslidable respectively in the X and the Y directions on the top of theconvex units 121 i and 121 j on the support frame 120. Note that anelastic member (leaf-spring, spring, etc.) for pressing the imagedistortion correction plate with a predetermined force against each ofthe convex units on the support frame 120 is arranged in the upper spacein the periphery of the image distortion correction plate G, althoughthis is not shown in this figure.

The support frame 120 shown in FIG. 23 is mounted on a support frameholding member 130 shown in FIG. 24. FIG. 24 is a partial sectional viewshowing the structure of the upper portion of the projection opticalsystem PL. The holding member 130 is fixed via a plurality of spacers135 a and 135 b not to move in the upward/downward direction (Zdirection) and the X and the Y directions from the top of the lensbarrel of the projection optical system PL.

Furthermore, on the holding member 130, an aperture which does not shadethe field of the projection optical system PL is formed, and a pluralityof reference members 131 a and 131 b which align the support frame 120in the X, Y, and e directions are arranged on its upper surface. Stillfurther, upward/downward driving elements 133 a, 133 b, and 133 c (133 cis not shown in the figure), which are implemented by a direct-actingpiston or piezo element, etc. and are intended for infinitesimallytilting the support frame 120 against the X-Y plane, and driving units132 a, 132 b, and 132 c (132 c is not shown in the figure) which drivethe respective driving elements 133 a, 133 b (and 133 c) are arranged inthree locations under the holding member 130.

Each of the driving units 132 a, 132 b (and 132 c) moves each of thedriving elements 133 a, 133 b (and 133C) upward and downward by anoptimum amount in response to the control instruction from a tiltcontrol system 137, and tilts the support frame 120, that is, the imagedistortion correction plate G1 by a predetermined amount in apredetermined direction. The tilt direction and amount are determined bythe main control system 32 based on preset information prestored in themain control system 32 shown in FIG. 1, or the result of there-measurement of the distortion characteristic after the imagedistortion correction plate G1 is installed. Additionally, the drivingelements 133 a and 133 b (133 c) in the three locations are arranged onthe circumference having a predetermined radius with the optical axis ofthe projection optical system P1 as its center at an angle ofapproximately 120°, viewing on the X-Y plane. By simultaneously movingthe driving elements 133 a, 133 b (and 133 c) upward and downward, alsothe interval (“Hr” shown in FIG. 20) between the image distortioncorrection plate G1 and the reticle R can be adjusted.

The lens element G2 within the projection optical system PL, which isshown in FIG. 24, is arranged to be movable upward and downward alongthe optical axis AX of the projection optical system PL or to betiltable also as shown in FIG. 1, and can correct the magnificationerror of an image projected onto the wafer W and a symmetricaldistortion aberration (a spool-shaped, a barrel-shaped, atrapezoid-shaped distortion, etc.), which occurs within the entireeffective projection area EIA.

When thus polished image distortion correction plate G1 is put back inthe initial position in the projection optical path, that is, thearrangement position where the distortion characteristics before thepolishing process are measured, the distortion characteristics arere-measured using the test reticle and it is examined whether or not thedynamic distortion characteristics become those shown in FIG. 17B.

Note that, however, the distortion components which can befunction-approximated are superposed in the above example of FIG. 17B asstated above. Therefore, the distortion components which can befunction-approximated must be finally reduced almost to “0” with theinfinitesimal adjustment of the magnification by the tilt of the imagedistortion correction plate G1, by the upward/downward movement or theinfinitesimal tilt of the lens element G2, or by the pressure control.Then, how much the dynamic distortion characteristic that is re-measuredafter being reduced to “0” includes a random component is examined. Ifthe random component is within the standard range, the sequence of themanufacturing process of the image distortion correction plate G1 iscompleted.

In the meantime, the random component included in the dynamic distortioncharacteristic is not within the standard value, simulation is againperformed by using the computer 107 shown in FIG. 22 based on the dataof the re-measured distortion error, and the image distortion correctionplate G1 is again polished depending on need.

As described above, in this embodiment, attention is paid not to thestatic distortion characteristic (distortion aberration characteristic)within the effective projection area EIA at the time of scan-exposure,but to the dynamic distortion characteristic caused by the accumulation(averaging) over the width of the scanning direction of the projectionarea EIA, and the image distortion correction plate G1 is polished tocorrect mainly the random component included in the dynamic distortioncharacteristic. Therefore, compared with the case where the imagedistortion correction plate G1 is polished to minimize the imagedistortion vector, for example, at all of the 13×7 ideal lattice pointswithin the effective projection area EIA, the polishing processsignificantly becomes easier, which leads to an advantage that also thesurface joint of the polished areas can be performed with highprecision.

Furthermore, in this embodiment, it becomes possible to set thepolishing areas on the image distortion plane G1, which are required toimplement the state where the dynamic distortion characteristic isreduced to “0” or is approximated to a predetermined function, apart sothat unnaturally joined surface portions are reduced in adjacentpolishing areas, which leads to the minimization of the deterioration ofthe local image quality of an image projected by the projection opticalsystem PL.

Notice that, the surface joint means the operations for smoothly joiningall the surfaces of a plurality of polished adjacent areas, which areobtained by polishing the respective surfaces under a condition that isslightly modified from a primarily condition determined in acalculation, so that the image distortion vector, which occurs due tothe simultaneous passage of the image formation luminous flux from anobject point on the reticle R through a plurality of adjacent polishedareas, is not unnaturally corrected depending on the position of theobject point in the X-Y direction on the reticle R.

The above described embodiment is dedicated to the explanation about themanufacturing and adjustment methods of the image distortion correctionplate G1. However, when the image distortion correction plate G1 ismanufactured, static distortion errors must be precisely measured at aplurality of ideal lattice points by using a test reticle as describedabove. The measurement of such distortion characteristics may be madewith the method using the image detector KES shown in FIG. 1, other thanthe method using test printing.

Therefore, the distortion measurement using the image detector KES isbriefly explained by referring to FIG. 25. FIG. 25 shows theconfiguration of the image detector KES mounted on the wafer table TB ofthe exposure apparatus, and the configuration of the signal processingsystem relating thereto. In this embodiment, the coordinate position ofthe test pattern image projected from the projection optical system PLis obtained by using the knife-edge measurement method.

In FIG. 25, the image detector KES comprises: a shading plate 140 whichis arranged to be almost as tall as (for example, in a range of ±1 mm orso) the surface of the wafer W on the table TB; a rectangular aperture(knife-edge aperture) of approximately several tens to several hundredsof μm, which is formed in a predetermined position on the shading plate140; a quartz optical pipe 142 into which the image formation luminousflux from the projection optical system PL, which passes through theaperture 141, enters with a large NA (numerical aperture); and asemiconductor reception element (silicon photodiode, PIN photodiode,etc.) 143 which photoelectrically detects the light quantity of theimage formation luminous flux transmitted by the optical pipe 142 withalmost no loss.

The surface of the image detector KES is set to almost agree with theimage formation plane of the projection optical system PL, when thetable TB is set in the center of the entire moving stroke (for example,1 mm) in the Z direction.

In the above described configuration of the image detector KES, theshading plate 140 is configured by coating a chromium layer onto thesurface of a quartz or fluorite plate having a high transparency ratiofor the light in an ultraviolet range and by forming the aperture 141 ina portion of the chromium layer, while the optical pipe 142 isconfigured by gathering many quartz optical fibers as a bundle having anentire thickness of approximately several millimeters, or by cuttingquartz into a long and thin square pillar the section of which is asquare and making its inside into an entire reflection plane.

If the shading plate 10 and the reception element 143 are spatiallyarranged apart with such an optical pipe 142, the influence on thereception element 143 with the temperature rising of the shading plate140, which is caused by the irradiation of the image formation luminousflux on the shading plate 140 for a long time, can be reduced. As aresult, it becomes possible to keep the temperature of the receptionelement 143 almost constant, and at the same time, it becomes possibleto allow the image formation luminous flux passing through the aperture141 to be received without any loss.

In the meantime, for the projection image detection using the imagedetector KES, the laser interferometer 62 shown in FIG. 1 is used. Thelaser interferometer 62 is configured by a laser beam source 62A thefrequency of which is stabilized, beam splitters 62B and 62C which splitthe laser beam toward a movable mirror 60 fixed on the table TB and areference mirror 62E fixed to the lower portion of the lens barrel ofthe projection optical system PL, and a receiver 62D for receiving thebeams which are respectively reflected by the movable mirror 60 and thereference mirror 62E and interfere with each other at the beam splitter62B, etc. as shown in FIG. 25.

The receiver 62D comprises a high-speed digital counter whichincrementally counts the move amount of the table TB based on thephotoelectric signal according to the change of the fringe of aninterfering beam by the resolution of 10 nm, and transmits the digitalvalue counted by the counter to the wafer stage control system 58 shownin FIG. 1 as the coordinate position of the table TB (wafer W) in the X(or Y) direction.

If the illumination light for exposure is obtained from the excimerlaser light source 1 as shown in FIGS. 1 and 13, the photoelectricsignal from the reception element 143 of the image detector KES becomesa pulsed waveform in response to the pulsed light emission of theexcimer laser light source 1. That is, assuming that the image opticalpath from a certain object point on the test reticle arranged on theobject plane of the projection optical system PL is MLe as shown in FIG.25, the excimer laser light source 1 shown in FIG.1 is made topulsed-light-emit in the state where the table TB (that is, the waferstage 14) is aligned in the X and the Y directions in order to make theimage optical path MLe agree with the rectangular aperture 141 of theimage detector KES, so that also the photoelectric signal from thereception element 143 becomes a pulsed waveform with the time intervalof approximately 10 to 20 ns.

Accordingly, the photoelectric signal from the reception element 143 isconfigured to be input to a sample/hold (hereinafter referred to as S/H)circuit 150A having an amplification operation shown in FIG. 25, and theS/H circuit 150A is configured to be switched between the sample and thehold activities in response to every 1-nm pulse signal for counting,which is generated by a receiver 62E in the laser interferometer 62.

Then, the control system 2 of the excimer laser light source 1 shown inFIG. 1 triggers pulsed light emission according to the coordinateposition information transmitted from the laser interferometer 62 to thesynchronization control system 66 and the main control system 32 in FIG.1 via the stage control system 58. Namely, this embodiment is configuredso that the pulsed light emission of the excimer laser light source 1 isperformed according to the coordinate position of the table TB, and theS/H circuit 150A holds the peak value of the pulse signal waveform fromthe reception element 143 in synchronization with the pulsed lightemission.

The peak value held by the S/H circuit 150A is converted into a digitalvalue by an analog-to-digital (A-D) converter 152A, and the converteddigital value is stored in a waveform memory circuit (RAM) 153A. Anaddress when the RAM 153A performs a storage operation is generated byan up/down counter 151 which counts every 10-nm pulse signal forcounting transmitted from the laser interferometer 62, and the moveposition of the table TB and the address when the RAM 153A performs astorage operation are nonambigously corresponded to each other.

In the meantime, the peak intensity of the pulsed light from the excimerlaser light source 1, has a fluctuation of approximately several percentfor each pulse. Therefore, in the processing circuit in this embodiment,a photoelectric detector 155 for detecting an intensity is arrangedwithin the illumination optical system (7A to 7Q) shown in FIG. 1 inorder to prevent the image measurement accuracy from being deteriorateddue to this fluctuation. The photoelectric signal (pulsed waveform) fromthe photoelectric detector 155 is captured by an S/H circuit 150B, anA-D converter 152B, and a RAM 153B (the address generation at the timeof the storage operation is common to that of the RAM 153A), which arerespectively equivalent to the above described S/H circuit 150A, the A-Dconverter 152A, and the RAM 153A.

In this way, the peak intensity of each pulsed light from the excimerlaser light source 1 is stored in the RAM 153B in the state where themove position of the table TB and the address at the time of the storageoperation of the RAM 153B are nonambigously corresponded.

The photoelectric detector 155 uses the mirror 7J within theillumination optical system shown in FIG. 1 as a partial transparentmirror, and is arranged to receive the pulsed light of approximately 1to several percent, which passes through the rear side of the mirror 7Jthrough a collective lens. If the photoelectric detector 155 is arrangedin such a position, it serves also as a light quantity monitor forcontrolling the amount of exposure when each shot area on the wafer W isexposed.

As described above, the digital waveform stored in the RAM 153A or 153Bis read into a waveform analyzing computer (CPU) 154, and the measuredwaveform according to the image intensity stored in the RAM 153A isstandardized (divided) by the intensity fluctuation waveform of theillumination pulsed light stored in the RAM 153B. The standardizedmeasured waveform is temporarily stored in the memory within the CPU154, and at the same time, the central position of the image intensityto be measured is obtained by respective types of a waveform processingprogram.

In this embodiment, a test pattern image on the test reticle is detectedwith the edge of the aperture 141 of the image detector KES. Therefore,the central position of the image, which is analyzed by the CPU 154, isobtained as the coordinate position of the table TB (wafer stage 14)measured by the laser interferometer 62, when the center of the testpattern image and the edge of the aperture 141 agree with on the X-Yplane.

The information of thus analyzed central position of the test pattern istransmitted to the main control system shown in FIG. 1. The main controlsystem 32 instructs the control system 2 of the excimer laser lightsource 1 and the wafer stage control system 58 in FIG. 1, and the CPU154 in FIG. 25 of the operations for sequentially measuring the positionof each projection image of the test pattern formed at a plurality ofpoints (for example, ideal lattice points) on the test reticle.

Here, the test reticle TR preferable for this embodiment is brieflyexplained by referring to FIG. 26. FIG. 26 is a plan view showing theentire pattern layout on the test reticle TR, and assumes that thecenter of the test reticle TR is the origin of the X-Y coordinatesystem. The direction of scan-exposure is the Y direction also in FIG.26. On the left side of the test reticle TR in FIG. 26, also theeffective projection area EIA indicated by a broken line is shown. Bothends of the effective projection area EIA in the non-scanning (X)direction are set to agree with the respective two sides, which extendin the Y direction, of the shading band LSB enclosing the pattern areaof the test reticle TR as a rectangle.

Outside the shading band LSB of the test reticle TR, cross-shapedreticle alignment marks RMa and RMb are formed. The marks RMa and RMbare detected by a microscope for reticle alignment in the state wherethe test reticle TR is put on the reticle stage 8 (see FIG. 1) of theexposure apparatus, so that the test reticle TR is aligned with thereference points within the apparatus.

Inside the shading band LSB of the test reticle TR, test pattern areasTM(i,j), which are arranged in a matrix state with a predeterminedpitch, are formed. Each of the test pattern areas TM(i,j) is formed by arectangular shading layer (an oblique line portion) the entire size ofwhich is approximately 1 to 2 mm, as expanded and shown in the lowerportion of FIG. 26. In the shading layer, a Line & Space (L&S) patternMX(i,j) having a periodicity in the X direction cycle and a L&S patternMY(i,j) having a periodicity in the Y direction cycle are formed to bedetected by the image detector KES. Also a LAMPAS mark MLP or a verniermark Mvn, which are used to examine the resolution or the alignmentprecision, are formed in a transparent window MZ.

Additionally, shading parts TSa and TSc of a predetermined size aredesigned to be secured on both sides of the L&S pattern MX(i,j) in the Xdirection in the rectangular shading layer of the test pattern areaTM(i,j). The squares of the shading parts TSa and TSc are set to belarger than that of the rectangular aperture 141 of the image detectorKES on the projection image plane side. Similarly, shading parts TSa andTSb of the predetermined size are secured also on both side of the L&Spattern MY(i,j) in the Y direction.

It is assumed that the L&S patterns MX(i,j) and MY(i,j) shown in FIG. 26have 10 transparent lines in the shading layer, and the width of theshading line between transparent lines and that of each transparent lineare the same. However, the number of transparent lines, the ratio (duty)of the width of a transparent line to that of a shading line, etc. maybe arbitrarily set. Note that the width of each transparent line in thecycle direction is set to be sufficiently resolvable by the projectionoptical system PL, and not to be extremely thick. By way of example, theline width is set in a range from Δr to 4Δr, which can be resolved bythe projection optical system PL.

When the test reticle TR shown in FIG. 26 is put on the reticle stage 8of the exposure apparatus and aligned, the position of the wafer stage14 is determined to be located in one test pattern area TM(i,j) to bemeasured by the rectangular aperture 141 of the image detector KES, asshown in FIG. 27.

FIG. 27 shows the positional relationship immediately before therectangular aperture 141 scans the projection image MYS(i,j) of the L&Spattern MY(i,j) within one test pattern TM(i,j) in the Y direction. Inthe state shown in FIG. 27, the rectangular aperture 141 is completelyshaded by the shading part TSb (or TSa) shown in FIG. 26. Therectangular aperture 141 moves from this position in FIG. 27 toward afirst slit image (transparent line image) Ms1 in the right directionalmost at a constant speed.

At this time, the level of the photoelectric signal from the receptionelement 143 changes so that it rises the moment that an edge 141A on theright side of the rectangular aperture 141 traverses the first slitimage Ms1 (position “ya”), and falls to “0” the moment or after an edge141B on the right side of the rectangular aperture 141 traverses a tenthslit image Ms10 (position “yd”), as shown in FIG. 28.

FIG. 28 shows a signal waveform EV represented by taking the coordinateposition of the wafer stage 14 (rectangular aperture 141) in the Y (orX) direction as the horizontal axis, and the voltage level of thephotoelectric signal from the reception element 143 as the verticalaxis. The signal waveform EV increases in a stairs state as the firstslit image Ms1 to the tenth slit image Ms10 of the projection imageMYS(i,j) sequentially go into the rectangular aperture 141, and reachesa maximum value EVp at a position “yb”. Thereafter, when the wafer stage14 passes through a position “yc”, the signal waveform EV decreases in astairs state as the slit images go out of the rectangular aperture 141sequentially from Ms1 to Ms10.

A stepwise voltage change amount ΔVe configuring such a waveform EV inthe stairs state corresponds to the quantity of light of one of the slitimages within the projection image MYS(i,j). The important portions inthe position measurement using the signal waveform EV are the rising andthe falling portions between the respective steps. The signal waveformEV in the stairs state is temporarily stored in the RAM 153A in FIG. 25.Then, the correction (division) of the intensity fluctuation of eachillumination pulsed light is made by the CPU 154 for each data (voltagevalue) at each address in the RAM 153A.

Thus standardized signal waveform EV is further smoothed by the CPU 154,and the smoothed signal waveform is differentiated so that the risingand the falling positions between the respective steps are emphasized.Since the differentiated waveform is a rising waveform between therespective steps of the signal waveform EV again shown in FIG. 29(A) inthe interval from the position “ya” to the position “yb” as shown inFIG. 29(B), it becomes a positively differentiated pulse. Additionally,since the waveform is a falling waveform between the respective steps ofthe signal waveform EW in the interval from the position “yc” to theposition “yd”, it becomes a negatively differentiated pulse. FIG. 29(A)again illustrates FIG. 8 for ease of understanding of the correspondencebetween the positions on the differentiated pulse waveform in FIG. 29(B)and the respective step positions on the original signal waveform EV.

After the CPU 154 shown in FIG. 25 makes a correspondence between thedifferentiated waveform shown in FIG. 29(B) and the Y (or X) coordinateposition and stores the correspondence in its internal memory, itcalculates the gravity center positions Yg1, Yg2, . . . , Yg20 forrespective 20 pulses in the differentiated waveform, and determines theposition YG(i,j) obtained by adding and averaging the respectivepositions Yg1 to Yg20. This position YG(i,j) is the Y coordinate valueof the wafer stage 14, which is measured by the laser interferometer 62when the central point of the projection image MYS(i,j) in the Ydirection in FIG. 27 perfectly agrees with the median point of thesegment linking the two edges 141A and 141B of the rectangular aperture141.

As described above, the Y coordinate position of the projection imageMYS(i,j) of each L&S pattern MY(i,j) within the test pattern areasTM(i,j) formed at the plurality of locations on the test reticle TR issequentially measured. Also the X coordinate position of the projectionimage MXS(i,j) of each L&S pattern MX(i,j) within the test pattern areasTM(i,j) is measured with the exactly the same procedures.

In this case, the rectangular aperture 141 of the image detector KES isscanned in the X direction for the projection image MXS(i,j), and a pairof edges 141C and 141D which stipulate the width of the rectangularaperture 141 in the X direction in FIG. 27 operate as a knife-edge forthe projection image MXS(i,j). Accordingly, the waveform EV of thephotoelectric signal from the reception element 143 and itsdifferentiated waveform are exactly the same as those shown in FIGS.29(A) (B). However, since the central position XG(i,j) of the projectionimage MXS(i,j) in the X direction must be obtained, the pulse signal forcounting from the receiver 62D within the laser interferometer 62 shownin FIG. 25 is switched to the pulse signal for counting, which isobtained from the receiver within the laser interferometer (16X in FIG.13) measuring the move position of the wafer stage 14 in the Xdirection.

In this way, the projection coordinate position [XG(i,j),YG(i,j)] at theideal lattice point stipulated by the L&S patterns MX(i,j) and MY(i,j)within each test pattern area TM(i,j) on the test reticle TR can bemeasured. By obtaining the difference in the X-Y direction between themeasurement result and the coordinate position of each ideal latticepoint on the test reticle TR, the static image distortion vectorDV(Xi,Yj) at each ideal lattice point, which explained in FIGS. 14 or15, can be obtained.

With the above described distortion measurement method, the static imagedistortion vector DV(Xi,Yj) is obtained after measuring each projectioncoordinate position [XG(i,j),YG(i,j)] of the L&S patterns MX(i,j) andMY(i,j). However, the image distortion vector DV(Xi,Yj) can be obtainedwithout actually measuring each projection coordinate position[XG(i,j),YG(i,j)].

That is, the coordinate position of the ideal lattice point stipulatedby the L&S patterns MX(i,j) and MY(i,j) on the test reticle TR is knownbeforehand in a design, also the projection image position (idealprojection position) when the ideal lattice point is projected throughan ideal projection optical system PL is known beforehand in the design.Therefore, by way of example, at the stage where the differentiatedwaveform shown in FIG. 29(B) is generated in a memory, the referenceaddress corresponding to the ideal projection position among theaddresses in the memory is set by software, the position obtained byadding and averaging the respective gravity center positions of the 20pulses of the differentiated waveform shown in FIG. 29(B) is determinedas an identified address in the memory, and the difference value betweenthe identified address and the above described reference address ismultiplied by the value of the resolution (such as 10 nm) of themeasurement pulse signal from the laser interferometer 62 (or 16X), sothat the image distortion vector DV(Xi,Yj) can be directly calculated.

For the above described projection image detection using the imagedetector KES, there is a matter to be further considered. The matter isthat the intensity distribution of unnecessary interference fringes issuperposed on the intensity distribution of the pulsed illuminationlight irradiated on the reticle R with a contrast of several percent orso due to the use of the first and the second fly-eye lenses 7C and 7Gshown in FIG. 1.

Therefore, When the wafer W is scan-exposed, the vibration mirror 7Darranged between the first and the second fly-eye lenses 7C and 7G inFIG. 1 is vibrated, a plurality of pulsed illumination lights areirradiated while deflecting the pulsed illumination light incident onthe second fly-eye lens 7G by an infinitesimal amount in thenon-scanning direction intersecting the moving (Y) direction of thereticle R at the time of scan-exposure, and the interference fringes isinfinitesimally moved in the non-scanning direction on the reticle R(and the wafer W) for each of the plurality of pulsed illuminationlights, so that the contrast of the interference fringes superposed onthe pattern image which is projected and exposed onto the wafer W issufficiently decreased by the accumulation effect of the resist layer.

However, the accumulation effect by the resist layer cannot be used whena projection image is detected with the image detector KES, unlike thecase of the scan-exposure of the wafer W. Therefore, it is desirable toobtain a similar accumulation effect, for example, by a hardware processwith the circuit configuration where the signal processing circuit inFIG. 25 is partially changed, or by a software process using the CPU154.

Specifically, the method for sufficiently reducing the moving speed whenthe projection image MYS(i,j) or MXS(i,j) of the L&S pattern is scannedwith the rectangular aperture 141 as shown in FIG. 27, and for providinga plurality of trigger signals to the control system 2 of the excimerlaser light source 1 in response to one pulse of the pulse signal forcounting from the laser interferometer 62 (or 16X in FIG. 13) in thestate where the vibration mirror 7D is vibrated at high speed, can beadopted.

Therefore, the method for obtaining the accumulation effect by thehardware process is briefly explained by referring to FIGS. 30 and 31.First of all, for example, 3 trigger pulses TP1, TP2, and TP3 areconfigured to be generated in response to one pulse of the pulse signalCP for counting from the laser interferometer 62 (or 16X) intended tomeasure the position of the wafer stage 14 as shown in FIG. 30, and theexcimer laser light source 1 is made to oscillate in response to therespective trigger pulses TP1, TP2, and TP3.

Then, part of the signal processing circuit shown in FIG. 25 is changedto that shown in FIG. 31. In FIG. 31, the circuit is configured in a waysuch that an accumulator 157A which adds the output data of the A-Dconverter 152A and the data temporarily stored in a register 157B isconnected next to the A-D converter 152A which converts the peak valueof the photoelectric signal from the reception element 143 of the imagedetector KES into a digital value, and the result of the addition isstored in a RAM 253A similar to that shown in FIG. 25.

Additionally, the circuit is configured in a way such that asynchronization circuit 157C which outputs the trigger pulses TP1, TP2,and TP3 in response to the pulse signal for counting CTP from theinterferometer is arranged to synchronize sequences, and the sample andthe hold operations of the S/H circuit 150A are switched according tothe respective trigger pulses TP1, TP2, and TP3. These trigger pulsesTP1, TP2, and TP3 are transmitted also to the accumulator 157A, whichsequentially adds the data output from the A-D converter 152A everythree trigger pulses TP1, TP2, and TP3 (every three pulsed lightsemission).

In such a configuration, the register 157B operate to be reset to “0” atthe rising edge of the pulse signal for counting CTP from theinterferometer, and the synchronization circuit 157C outputs the firsttrigger pulse TP1 after the register 157B is reset to “0”. The S/Hcircuit 150A and the A-D converter 152A begin to operate in response tothe output trigger pulse TP1. Then, the peak value EV1 of the signaloutput from the reception element 143 according to the first pulsedlight emission is applied to one of input terminals of the accumulator157.

Since the data of the register 157B is “0” at this time, the peak valueEV1 emerges in the output of the accumulator 157A. This output isimmediately transmitted to the register 157B and stored. After apredetermined amount of time elapses, the synchronization circuit 157Coutputs the second trigger pulse TP2. Then, the peak value EV2 of thesignal output from the reception element 143 according to the secondpulsed light emission is applied to one of the input terminals of theaccumulator 157A in a similar manner.

As a result, the addition value of the peak value EV2 from the A-Dconverter 152A and the peak value EV1 from the register 157B emerges inthe output of the accumulator 157A, and this addition value is againtransmitted to the register 157B. Similar operations are performed alsofor the third trigger pulse TP3. Consequently, the addition value of thepeak values EV1, EV2, and EV3 which are respectively obtained by thethree pulsed light emissions emerges in the output of the accumulator157A, and this addition value is stored at a specified address in theRAM 153A.

In the above described embodiment, the three trigger pulses TP1, TP2,and TP3 are generated for one pulse of the pulse signal for countingfrom the interferometer. While these trigger pulses are generated, theangle of the vibration mirror 7D is infinitesimally changed. Therefore,the contrast component of the interference fringes superposed for eachpulsed light emission on the image MXS(i,j) or MYS(i,j) projected ontothe shading plate 140 of the image detector KES, is averaged, wherebythe distortion of the signal waveform EV shown in FIG. 28 due to theinterference fringes is reduced.

Except for the above described method, there are methods for reducingthe precision deterioration due to the interference fringes when animage is measured using the image detector KES. One of them is a methodfor scanning the rectangular aperture 141 of the image detector KES aplurality of times for one projected L&S pattern image MXS(i,j) orMYS(i,j). In this case, the signal processing circuit is assumed to bethe above described circuit shown in FIG. 25, the waveform process likethe one shown in FIG. 29(A) (B) is performed in each of the plurality oftimes of the scanning for the rectangular aperture 141, and the centralposition (or the image distortion vector) of the projection image isaveraged on the software of the CPU 154 after the central position (orthe image distortion vector) is obtained for each scanning.

Since the angle of the vibration mirror 7D is infinitesimally changedwhile the rectangular aperture 141 is scanned a plurality of times asdescribed above, the position of the interference fringes isinfinitesimally shifted in each scanning for the rectangular aperture141. As a result, the central position (or the image distortion vector)of the projection image which can possibly scatter and be measured dueto the influence of the interference fringes contrast can be averagedand obtained, thereby improving the measurement accuracy that much.

In the above described configuration, the wafer stage 14 is scanned inthe X or the Y direction when a projection image is detected with theimage detector KES. However, a similar distortion measurement can bemade also by making the image detector KES stationary at a certainmeasurement position, and by infinitesimally moving the reticle R in theX or the Y direction. Additionally, the image detector KES (wafer stage14) and the reticle R may be synchronously moved at a speed ratedifferent from the initial speed rate, for example, in the Y direction(scan-exposure direction), and the signal waveform obtained from thereception element 143 may be analyzed during that time period.

In this case, both of the rectangular aperture 141 and the projectionimage MYS(i,j) move in one direction along the Y direction with aconstant speed difference, and the projection image MYS(i,j) isrelatively scanned by the rectangular aperture 141 by the speeddifference, so that also the signal from the reception element 143becomes the waveform in a stairs state. When both of the reticle R andthe image detector KES are synchronously moved as described above,strictly speaking, the static distortion characteristic at an ideallattice point is not truly measured. However, if the waveform of thephotoelectric signal at that time is analyzed, the averaged imagedistortion vector in a local range, where the L&S pattern projectionimage MYS(i,j) is scanned and moved within the projection field IF, thatis, the dynamic distortion characteristic can be known.

When the image distortion correction plate G1 is polished with thepolishing processor shown in FIG. 22 based on the result of the abovedescribed automatic measurement, not only one side of the imagedistortion correction plate G1 as shown in FIG. 20, but both of itssides may be polished as show in FIG. 32. FIG. 32 exaggeratingly showspart of the section of the image distortion correction plate G1 throughwhich the image formation luminous flux LB′(1,1) from one lattice pointGP(1,1) on the reticle R or the test reticle TR passes.

In the case of FIG. 32, polishing areas S′(1,1) and S′(0,1) are set onthe back surface of the image distortion correction plate G1 (on theprojection optical system PL side) in correspondence with polishingareas S(1,1) and S(0,1) on the front surface. Also each of the polishingareas S′(1,1) and S′(0,1) on the back surface is polished to be a slopeof a wavelength order in order to give an infinitesimal deflection angleoptimum for the image formation luminous flux (principal ray).

By way of example, the image formation luminous flux LB′(1,1) shown inFIG. 32 is deflected by the two infinitesimal slopes of the polishingareas S(1,1) and S′(1,1). Accordingly, if the tilt directions andamounts of the polishing areas S(1,1) and S′(1,1) are set to be almostthe same, only the local areas can be modified on a tilted parallelplate, so that the deflection-corrected principal ray MB′(1,1) can berestored to be almost parallel to the optical axis AX. Therefore, thereis an advantage that the principal ray MB′(1,1) from the object pointGP(1,1) becomes almost vertical to the projection image plane of theprojection optical system PL, and the telecentric state is maintained.

Additionally, if both sides of the image distortion correction plate G1are polished, a plurality of adjacent polishing areas which cannot butoverlap among the polishing areas S(i,a) and S(i,b) can be separated onthe front and the back surfaces of the image distortion correction plateG1 even if they exist, as explained earlier by referring to FIG. 21. Asa result, there is an additional advantage that the joining of thepolished planes on the same surface becomes smooth, which leads to theimplementation of a more precisely distortion correction.

According to the above described embodiment, optical correction members(G1, G3, G4, etc.) to be inserted in the projection optical path betweenthe mask (reticle R) and the substrate to be exposed (wafer W) arepolished by using the dynamic aberration information which is added andaveraged, and specific to the scan-exposure, thereby obtaining an effectof allowing the surface shapes and the areas of the optical correctionmembers to be designed with high precision.

Furthermore, since also the surface shape to be polished can be muchmoderately set, a significant effect of improving the polishingprocessing accuracy can be obtained.

According to the above described embodiment, a satisfactory correctioncan be made also to the aberrations such as an astigmatism/comacharacteristic, image plane curvature, or a telecentric error other thanthe distortion characteristic among the various aberrationcharacteristics which become problems in the case of the scan-exposuremethod.

Normally, the astigmatism aberration occurring in the case of the staticexposure method can be corrected by infinitesimally tilting to the planevertical to the projection optical axis the parallel plate (quartz,etc.) inserted between the lens element which is closest to the imageside in the projection optical system and the substrate to be exposed.

In the case of the scan-exposure method, the area contributing to theexposure within the projection field is a rectangular slit shape or anarc-slit shape. Moreover, considering that the astigmatismcharacteristic which is added and averaged in the scanning directionbecomes dynamic, the dynamic astigmatism aberration may increase in thecenter portion of the slit-shaped projection area, or non-linear (orrandom) astigmatism may occur in some cases.

Accordingly, it becomes possible to make an astigmatism correction withhigh precision by locally modifying the surface of the astigmatism/comacorrection plate arranged in the neighborhood of the image plane in theoptical path of an exposure light, whereby an effect of removing theseaberrations can be obtained.

Furthermore, the image plane curvature among the respective opticalaberrations can be corrected by replacing the lens element having a longcurvature radius, which is arranged between the projection opticalsystem and the substrate to be exposed, with a lens element of the samediameter having a slightly different curvature radius, in the case ofthe static exposure method.

In the case of the scan-exposure method, since the static image planecurvature characteristic is added and averaged in the scanningdirection, a non-linear (random) image plane curvature error, whichcannot be modified only by correcting the image plane tilt and the imageplane curvature with replacement of lens elements in the static exposuremethod, can possibly remain.

According to the above described embodiment, an image plane curvaturecorrection plate which can correct a non-linear (random) image planecurvature error with high accuracy, can be generated, whereby theprojection image plane by the projection optical system can be made intoa parallel plane which is entirely or locally even, and a DOF (Depth ofFocus) can be significantly improved.

Additionally, the technique for correcting respective aberrationcharacteristic types or the technique for manufacturing correctionplates in the above described embodiment is essential especially when acircuit pattern having a minimum line width of 0.08 to 0.2 μm or so isprojected and exposed onto the substrate to be exposed to which aplanarization technique is applied through a high-NA projection opticalsystem with the image side numerical aperture of 0.65 or more.

However, since the respective static aberrations within the projectionarea are averaged in the scanning direction in the scan-exposure methodexplained in the embodiments of this application, the aberration (imagequality) occurring in the image transferred onto the exposed substratecan possibly deteriorate in comparison with the portions within theprojection area, where the respective static aberrations are minimized.

Accordingly, the averaging in the state where an image deteriorationoccurs must not be performed. Therefore, the correction using areduction is made by infinitesimally moving the lens elements andoptical members so as to minimize the respective aberrations as littleas possible when the projection optical system itself is assembled oradjusted. Furthermore, the positions of the lens elements or the opticalmembers within the lens barrel are infinitesimally adjusted, etc. in thestate where the lens barrel of the projection optical system isinstalled in the body of the apparatus, and all possible efforts must bemade to remove a liner aberration (an aberration characteristic whichcan be function-approximated) from a calculation value.

Then, the optical correction members are processed to correct anaberration for the non-linear error (random component) which remainsafter the linear aberration is removed, whereby the linear and therandom aberration components can be suppressed almost to “0”.

As described above, in this embodiment, a dynamic distortioncharacteristic is determined based on the result of actual test printingwith a scan-exposure method. This method is applicable also to the casewhere the respective image formation aberration types such as a dynamictelecentric error characteristic, a dynamic astigmatism/comacharacteristic, etc. are measured, in exactly the same manner.Additionally, in this embodiment, a dedicated device for examining andmeasuring mark projection images TM′(i,j) at a plurality of positions ona test-printed wafer, or an alignment system of a projection exposureapparatus is required. However, since the position of a mark projectionimage which is actually formed on a resist layer, the resolution stateof a projection image, the difference due to the directionality of anL&S pattern image, etc. are actually measured, measurements based on theactual optical characteristics of the illumination optical system andthe projection optical system PL of the projection exposure apparatuscan be made.

The exposure apparatus according to this embodiment is applicable alsoto an exposure apparatus of a step-and-repeat type, which exposes apattern of a mask in a state where the mask and a substrate are madestationary, and sequentially stepmoves the substrate.

Additionally, as a projection optical system, a material which passes afar-ultraviolet ray through, such as quartz or fluorite, is used as aglass material when the far-ultraviolet light such as an excimer laser,etc. is used. If an F₂ laser or an X ray is used, an optical system suchas a catadioptric system or a dioptric system can be used. As a reticle,a reflection type my be used.

Furthermore, if a linear motor (refer to U.S. Pat. No. 5,623,853 or U.S.Pat. No. 5,528,118) is used for a wafer stage or a reticle stage, eitherof an air floating type using an air bearing and a magnetic floatingtype using Lorentz force or reactance force may be used. Still further,a stage may be of a type moving along a guide or of a guideless typehaving no guide.

Still further, the repulsion force generated by the moving of a waferstage may be mechanically freed to a floor (the earth) by using a framemember, as recited in the Japanese laid-open Publication No. 8-166475(U.S. Pat. No. 5,528,118).

Still further, the repulsion force generated by the moving of a reticlestage may be freed to a floor (the earth) by using a frame member, asrecited in the Japanese laid-open Publication No. 8-330224.

Optical adjustments are made by embedding the above describedillumination optical system and the projection optical system, which arecomposed of a plurality of optical elements, wires and pipes areconnected after a reticle stage and a wafer stage, which are composed ofmany mechanical parts, in an exposure apparatus itself, and overalladjustments (electricity adjustment, operation verification, etc.) arefurther made, so that the exposure apparatus according to thisembodiment can be manufactured. It is desirable to manufacture theexposure apparatus in a clean room where the temperature, the degree ofcleanliness, etc. are managed.

Still further, a semiconductor device is manufactured by: a step ofdesigning the functionality and the performance of the device; a step ofmanufacturing a wafer from a silicon material; a step of exposing areticle pattern onto a wafer with the above described exposure apparatusaccording to the embodiment; a step of assembling the device (includinga dicing process, a bonding process, a packaging process, etc.); and astep of making an examination.

As described above, according to the present invention, correctionoptical members (G1, G3, G4, etc.) which are locally polished to correctdynamic aberration characteristics are inserted in a projection opticalpath between a mask (reticle R) and a substrate to be exposed (wafer W)by using the dynamic aberration information which is inherent in ascan-exposure apparatus and is added and averaged in the scanningdirection, whereby a significantly high aberration correction accuracyat the time of exposure can be obtained.

Accordingly, the accuracy of distortion matching or mixing & matchingcan be kept to be several to several tens nm, when a plurality ofprojection exposure apparatuses are mixed and used at the time ofoverlay and exposure on a manufacturing line of a semiconductor device,whereby a significant effect of improving the yield of semiconductordevice manufacturing can be realized.

What is claimed is:
 1. An exposure apparatus exposing a substrate byprojecting an image of a pattern of a mask onto the substrate,comprising: a projection optical system, which is arranged between themask and the substrate, and which projects the image of the pattern ofthe mask onto the substrate; and an astigmatism correction plate whichcorrects a non-linear astigmatism characteristic of the image of thepattern, astigmatic aberration of the image at a plurality of positionswithin a projection area of said projection optical system having anon-linear relation with each other.
 2. The exposure apparatus accordingto claim 1, further comprising a measurement device, which is arrangedon an image plane side of said projection optical system, measuring theastigmatism aberration at each of the plurality of positions within theprojection area.
 3. The exposure apparatus according to claim 1, furthercomprising an image plane curvature correction member, which is arrangedbetween the mask and the substrate, correcting non-linear image planecurvature of the image of the pattern within the projection area of saidprojection optical system.
 4. The exposure apparatus according to claim1, further comprising: a distortion correction member, which is arrangedbetween the mask and the substrate, respectively correcting non-lineardistortions of the image of the pattern within the projection area ofsaid projection optical system.
 5. An exposure apparatus exposing asubstrate by projecting an image of a pattern of a mask onto thesubstrate, comprising: a projection optical system, which is arrangedbetween the mask and the substrate, and which projects the image of thepattern of the mask onto the substrate; and a coma correction plate,which is arranged between the mask and the substrate, which corrects anon-linear coma characteristic of the image of the pattern, comaticaberration of the image of a plurality of positions within theprojection area of said projection optical system having a non-linearrelation with each other.
 6. The exposure apparatus according to claim5, further comprising a measurement device, which is arranged on animage plane side of said projection optical system, measuring thecomatic aberration at each of the plurality of positions within theprojection area.
 7. The exposure apparatus according to claim 5, furthercomprising an image plane curvature correction member, which is arrangedbetween the mask and the substrate, correcting non-linear image planecurvatureof the image of the pattern within the projection area of saidprojection optical system.
 8. The exposure apparatus according to claim5, further comprising: a distortion correction member, which is arrangedbetween the mask and the substrate, respectively correcting non-lineardistortions of the image of the pattern within the projection area ofsaid projection optical system.
 9. A projection exposure apparatus whichscan-exposes a substrate with a pattern on a mask, comprising: aprojection optical system having a predetermined image formationcharacteristic; a driving mechanism which moves the mask and thesubstrate in a one-dimensional scanning direction relative to saidprojection optical system; a restricting mechanism that restricts animage of the pattern, which is projected on an image plane side of saidprojection optical system, to within a projection area having apredetermined width in the one-dimensional scanning direction; and atleast one optical correction element which is arranged within saidprojection optical system, and is optically processed to correct anaverage vector obtained by averaging image distortion vectors at aplurality of image points existing along the one-dimensional scanningwithin the projection area at each of a plurality of positions in anon-scanning direction intersecting the one-dimensional scanningdirection within the projection area.
 10. The apparatus according toclaim 9, wherein said optical correction element is arranged in atelecentric space where a principal ray becomes almost vertical to anobject plane or an image plane of said projection optical system in animage formation optical path of said projection optical system.
 11. Theapparatus according to claim 10, wherein said optical correction elementis made of a transparent optical glass material arranged at least one ofthe object plane side and the image plane side, and a surface portioncorresponding to the projection area of the transparent optical glassmaterial is optically processed to have a locally different surfaceshape in order to make the average vector at each of the plurality ofpositions in the non-scanning direction almost identical.
 12. Theapparatus according to claim 11, wherein the transparent optical glassmaterial is held in a state of being parallel to the object plane or theimage plane of said projection optical system, or a state of beingtilted relative to the object plane or the image plane.
 13. Theapparatus according to claim 11, wherein a surface shape of a surface ofthe transparent optical glass material is optically and locallyprocessed so that a random error component obtained by removing a linearerror component from the average vector at each of the plurality ofpositions in the non-scanning direction is within ±(Δr/10), if a minimumsize of a pattern image which can be resolved on the image plane sidethrough said projection optical system is Δr.